From BiblePortal Wikipedia

Hastings' Dictionary of the New Testament [1]

It is remarkable that ‘key’ in the concrete form does not occur in the apostolic writings. The four occurrence in Rev. are symbolical. There are certain passages in Acts where we should expect mention of a key, but the circumstances are exceptional, and ‘key’ is omitted ( Acts 12:10;  Acts 16:26-27). When a porter was in attendance, admittance was given from the inside, and a key to open was not necessary (cf.  Acts 12:14-15). From the fact that city gates were guarded, the need for a key was in this case also absent. It may be noted that the chains by which prisoners were secured, and the stocks in which their feet were made fast, were in all likelihood secured by the equivalent of a key ( Acts 12:6-7;  Acts 16:24 etc.).

We remark the difference between the Hebrew word (מַפְתֵּחַ), ‘that which opens ,’ and the Greek and Latin (κλείς, clavis ), ‘that which shuts .’ This seems to correspond with actual usage. Among the Hebrews the lock was arranged in such a manner that the key was requisitioned only for opening (see illust. in Hasting's Dictionary of the Bible (5 vols) ii. 836). The bar was shot, and the lock acted of itself, but it could be withdrawn only by aid of a key or opener. This advanced mode of making fast a door was doubtless preceded and attended by a simpler process, whereby the bolt or bar could be moved forwards and backwards by means of a hoot passing through a slit in the door. This served to shut the door, but did not make it absolutely secure as in the other case. For the age with which we have to deal we must think of the key as a device by which one outside held command over the closed door. Having shut it in the first instance, one had power to open it by applying the key.

The imagery of Rev., so far as ‘key’ is concerned, implies power and authority on the part of one standing outside and having possession of the key. This power is in the hands of angelic beings, who are above earth, and chiefly in the hands of the Risen Christ. Their dominion is manifested upon earth and in the under world, over living and dead.

(1) Christ has the keys of death and of Hades ( Revelation 1:18, Revised Version). This power is Imperial, exercised from without and from above. There are interesting parallels to this, apart from Scripture, in literature, both earlier and later. When Ištar descended to the land of no-return she called imperiously to the porter to open the door, and threatened in case of refusal to shatter the door and break the bolt. Here the power is primitively conceived, and remains largely with the one within. For later and more advanced conceptions see Dante, Purg . ix. 65ff., and Milton, Paradise Lost , ii. 774ff., 850ff. In both these instances the power, although great, is still limited.

(2) Angelic authority is evident in  Revelation 9:1;  Revelation 20:1, where the key of the ‘pit’ or ‘well’ of the abyss, or of the abyss simply, is spoken of. This power was delegated (‘was given,’ 9:1). That some symbol of power was bestowed seems clear from 20:1, where the key and a great chain for binding are seen in the angel’s hand (or attached to his person). The figure of the key here directs our thought to the pits or wells of ancient times, whose opening was safeguarded against illegitimate use by a covering of some kind. The primitive setting of such coverings would naturally be horizontal, but here the imagery, extending to key, points rather to a door set upright and secured by bolt or lock. The stone doors of tombs may be compared.

(3) Upon earth itself Christ’s unlimited authority is exercised over the churches, including that in Philadelphia ( Revelation 3:7). The ‘key of David’ here mentioned is reminiscent of  Isaiah 22:22, where some sort of investiture is in the writer’s mind ( Hasting's Dictionary of the Bible (5 vols) v. 172). In this instance power is exhibited in the most absolute form, and made over to the Church in the sense of a ‘door opened,’ for the enjoyment rather than for the extension of the gospel (see R. W. Pounder, Hist. Notes on the Book of Revelation , 1912, p. 140). It is not surprising that the reading of this verse should have been attracted to  Revelation 1:18, as appears in some inferior Manuscripts(ἅδον for Δαυείδ).

See further Dict. of Christ and the Gospels , article‘Keys.’ For specimens of actual keys discovered in the course of excavation see R. A. S. Macalister, The Excavation of Gezer , 1912, i. 187 and ii. 271. Further illustrations in A. Rich, Dict. of Roman and Greek Antiquities 3, 1873, s.v. ‘Clavis.’

W. Cruickshank.

Webster's Dictionary [2]

(1): ( n.) An indehiscent, one-seeded fruit furnished with a wing, as the fruit of the ash and maple; a samara; - called also key fruit.

(2): ( n.) A bar, pin or wedge, to secure a crank, pulley, coupling, etc., upon a shaft, and prevent relative turning; sometimes holding by friction alone, but more frequently by its resistance to shearing, being usually embedded partly in the shaft and partly in the crank, pulley, etc.

(3): ( n.) A wedge to unite two or more pieces, or adjust their relative position; a cotter; a forelock.

(4): ( n.) A simplified version or analysis which accompanies something as a clue to its explanation, a book or table containing the solutions to problems, ciphers, allegories, or the like, or a table or synopsis of conspicuous distinguishing characters of members of a taxonomic group.

(5): ( n.) A family of tones whose regular members are called diatonic tones, and named key tone (or tonic) or one (or eight), mediant or three, dominant or five, subdominant or four, submediant or six, supertonic or two, and subtonic or seven. Chromatic tones are temporary members of a key, under such names as " sharp four," "flat seven," etc. Scales and tunes of every variety are made from the tones of a key.

(6): ( n.) The fundamental tone of a movement to which its modulations are referred, and with which it generally begins and ends; keynote.

(7): ( v. t.) To fasten or secure firmly; to fasten or tighten with keys or wedges.

(8): ( n.) A piece of wood used as a wedge.

(9): ( n.) That part of a mechanism which serves to lock up, make fast, or adjust to position.

(10): ( n.) A position or condition which affords entrance, control, pr possession, etc.; as, the key of a line of defense; the key of a country; the key of a political situation. Hence, that which serves to unlock, open, discover, or solve something unknown or difficult; as, the key to a riddle; the key to a problem.

(11): ( n.) That part of an instrument or machine which serves as the means of operating it; as, a telegraph key; the keys of a pianoforte, or of a typewriter.

(12): ( n.) An instrument which is turned like a key in fastening or adjusting any mechanism; as, a watch key; a bed key, etc.

(13): ( n.) Fig: The general pitch or tone of a sentence or utterance.

(14): ( n.) The last board of a floor when laid down.

(15): ( n.) That part of the plastering which is forced through between the laths and holds the rest in place.

(16): ( n.) A metallic lever by which the circuit of the sending or transmitting part of a station equipment may be easily and rapidly opened and closed; any device for closing or opening an electric circuit.

(17): ( n.) A keystone.

(18): ( n.) An instrument by means of which the bolt of a lock is shot or drawn; usually, a removable metal instrument fitted to the mechanism of a particular lock and operated by turning in its place.

Vine's Expository Dictionary of NT Words [3]

1: Κλείς (Strong'S #2807 — Noun Feminine — kleis — klice )

"a key," is used metaphorically (a) of "the keys of the kingdom of heaven," which the Lord committed to Peter,  Matthew 16:19 , by which he would open the door of faith, as he did to Jews at Pentecost, and to Gentiles in the person of Cornelius, acting as one commissioned by Christ, through the power of the Holy Spirit; he had precedence over his fellow disciples, not in authority, but in the matter of time, on the ground of his confession of Christ ( Matthew 18:16 ); equal authority was committed to them ( Matthew 18:18 ); (b) of "the key of knowledge,"  Luke 11:52 , i.e., knowledge of the revealed will of God, by which men entered into the life that pleases God; this the religious leaders of the Jews had presumptuously "taken away," so that they neither entered in themselves, nor permitted their hearers to do so; (c) of "the keys of death and of Hades,"  Revelation 1:18 , RV (see HADES), indicative of the authority of the Lord over the bodies and souls of men; (d) of "the key of David,"  Revelation 3:7 , a reference to  Isaiah 22:22 , speaking of the deposition of Shebna and the investiture of Eliakim, in terms evidently Messianic, the metaphor being that of the right of entrance upon administrative authority; the mention of David is symbolic of complete sovereignty; (e) of "the key of the pit of the abyss,"  Revelation 9:1; here the symbolism is that of competent authority; the pit represents a shaft or deep entrance into the region (see Abyss from whence issued smoke, symbolic of blinding delusion; (f) of "the key of the abyss,"  Revelation 20:1; this is to be distinguished from (e): the symbolism is that of the complete supremacy of God over the region of the lost, in which, by angelic agency, Satan is destined to be confined for a thousand years.

King James Dictionary [4]

KEY, n. ke. In a general sense, a fastener that which fastens as a piece of wood in the frame of a building, or in a chain, &c.

1. An instrument for shutting or opening a lock, by pushing the bolt one way or the other. Keys are of various forms, and fitted to the wards of the locks to which they belong. 2. An instrument by which something is screwed or turned as the key of a watch or other chronometer. 3. The stone which binds an arch. See Key-stone. 4. In an organ or harpsichord, the key, or finger key is a little lever or piece in the fore part by which the instrument is played on by the fingers. 5. In music, the key, or key note, is the fundamental note or tone, to which the whole piece is accommodated, and with which it usually begins and always ends. There are two keys, one of the major, and one of the minor mode. Key sometimes signifies a scale or system of intervals. 6. An index, or that which serves to explain a cypher. Hence, 7. That which serves to explain any thing difficult to be understood. 8. In the Romish church, ecclesiastical jurisdiction, or the power of the pope, or the power of excommunicating or absolving. 9. A ledge or lay of ricks near the surface of the water. 10. The husk containing the seed of an ash.

KEY, n. A bank or wharf built on the side of a river or harbor, for the convenience of loading and unloading ships, and securing them in their stations. Hence keys are furnished with posts, rings, cranes, capstans, &c. It is sometimes written quay.

Wilson's Dictionary of Bible Types [5]

 Isaiah 22:22 (b) By this figure our Lord is describing the right of Jesus Christ to rule and to reign. He only can consign men to Heaven or to hell. He has never delegated this power to another. (See  Revelation 1:18).

 Matthew 16:19 The two keys given to Peter were evidently the two Gospels: one Gospel for the Jews which included baptism for the remission of sins; the other Gospel for the Gentiles in which salvation is by faith alone. By means of these two Gospel keys, Peter was used of GOD to bring thousands to Christ

 Luke 11:52 (b) This key is probably the person of the Lord Jesus Himself for when He is ignored, overlooked, or denied in the Scriptures, then there can be no knowledge of the truth of GOD, nor of the will of GOD.

 Revelation 1:18 (a) The Lord Jesus controls the destiny of the soul. He alone can send a man to hell. He alone decides the day of one's death. His will and decision in these matters is described as a key.

 Revelation 3:7 (a) This represents the right of the Lord JESUS to erect the throne of David again, to sit upon it, and to execute sovereign powers. This right is described as a key.

 Revelation 9:1 (a) The key in this passage represents the divine right and power given by GOD to the angel to open and close the pit of hell in order that the purposes of GOD might be performed.

Watson's Biblical & Theological Dictionary [6]

is frequently mentioned in Scripture, as well in a natural as in a figurative sense. The keys of the ancients were very different from ours; because their doors and trunks were closed generally with bands, and the key served only to loosen or fasten these bands in a certain manner. In a moral sense key has many significations: "And the key of the house of David will I lay upon his shoulder: so he shall open, and none shall shut; and he shall shut, and none shall open,"  Isaiah 22:22 ,—he shall be grand master and principal officer of his prince's house. Christ promises to St. Peter, that he should first open the gate of his kingdom, both to Jew and Gentile, in making the first converts among them,  Matthew 16:19 .

It is observable that no supremacy is here given to St. Peter; as the power of binding and loosing belonged equally to all the Apostles,  Matthew 18:18 . The term binding and loosing was customarily applied by the Jews to a decision respecting doctrines or rites, establishing which were lawful and which unlawful. ( See Bind . ) And it may also denote, to bind with sickness, and to loose by restoring to health. Jesus Christ says that he has the key of death and hell,  Revelation 1:18; that is, it is in his power to bring to the grave, or to deliver from it; to appoint to life or to death.

Hawker's Poor Man's Concordance And Dictionary [7]

I should not think it necessary to notice this, the thing is so familiar, were it not that the Lord Jesus hath condescended to use the figure with reference to his grace and power. He calls himself the "Key of David, who openeth and none shutteth; who shutteth and none openeth." ( Revelation 3:7;  Isaiah 22:22) It is blessed to see in how many ways the Lord manifests the supremacy of his power, He hath the key of heaven, to admit whom he pleaseth: he hath the key of hell, to shut up all his foes; he hath the key of his word, to unfold the mysteries of his kingdom; he hath the key of the heart, to open it, and to render that word effectual. Hence, in all things, from the highest heaven to the lowest hell, Jesus governs. What a sweet thought for all his redeemed to cherish! He it is that opens his church, opens the mouth of his ministers and the souls of his saints, opens the opportunities of ordinances, and gives blessings to ordinances, and the several means of grace upon earth, and finally; fully, and completely opens an entrance for all his redeemed into his everlasting kingdom in heaven. Gracious Lord Jesus, "open thou mine eyes, that I may see the wondrous things of thy law!"

Fausset's Bible Dictionary [8]

 Song of Solomon 5:4-5. A piece of wood, from seven inches to two feet long, fitted with pegs which correspond to small holes in the bolt within; the key put through a hole draws the bolt. The symbol of authority to open or shut ( Isaiah 22:22;  Revelation 3:7;  Revelation 1:18). A chamberlain's (eunuch) badge of office is often a key, hung by a kerchief "on the shoulders" ( Isaiah 9:6). The power of the keys was given to Peter and the other apostles only at times ( Matthew 16:19;  Matthew 18:18) when, and in so far as, Christ made him and them infallible. Peter rightly opened the gospel door to the Gentiles (Acts 10;  Acts 11:17-18;  Acts 14:27), but he wrongly tried to shut it again ( Galatians 2:11-18; compare  Luke 11:52).

Morrish Bible Dictionary [9]

Used symbolically for authority to open or to shut. Spoken of Eliakim, 'established by God,' as having the key of the house of David laid upon his shoulder: "he shall open, and none shall shut; and he shall shut, and none shall open."  Isaiah 22:22 . He is a type of the Lord Jesus, as spoken of in  Revelation 3:7 , who has also the keys of hades and of death.  Revelation 1:18 . To Peter were given the keys of the kingdom of heaven,  Matthew 16:19 , which he opened to the Jews in  Acts 2 , and to the Gentiles in  Acts 10 . The Lord charged the doctors of the law with taking away the key of knowledge.  Luke 11:52 . This they did by their traditions and by hindering those who would have entered in to the blessings brought by Christ.

Easton's Bible Dictionary [10]

Maphteah   Judges 3:25 Kleis   Matthew 16:19 Luke 11:52 Revelation 1:18 Isaiah 22:22

The word is used figuratively of power or authority or office ( Isaiah 22:22;  Revelation 3:7;  Revelation 1:8; comp 9:1; 20:1; Compare also  Matthew 16:19;  18:18 ). The "key of knowledge" ( Luke 11:52; Compare  Matthew 23:13 ) is the means of attaining the knowledge regarding the kingdom of God. The "power of the keys" is a phrase in general use to denote the extent of ecclesiastical authority.

Smith's Bible Dictionary [11]

Key. The key of a native Oriental lock is a piece of wood, from seven inches to two feet in length, fitted with the wires or short nails, which, being inserted laterally into the hollow bolt which serves as a lock, raises other pins within the staple so as to allow the bolt to be drawn back.

(Keys were sometimes of bronze or iron, and so large that one was as much as a man could carry. They are used in Scripture as a symbol of authority and power. Giving keys to a person signifies the intrusting of him with an important charge.  Matthew 16:19. In England, in modern times, certain officers of the government receive, at their induction into office, a golden key. - Editor).

Hastings' Dictionary of the Bible [12]

KEY . See House, § 6 . Of the passages where this word is used in a figurative sense the most important are   Isaiah 22:22 (cf.   Revelation 3:7 ), where the key is the symbol of authority and rule;   Luke 11:52 ‘the key of knowledge’; and the crux interpretum ,   Matthew 16:19 , for which see Power of the Keys.

A. R. S. Kennedy.

International Standard Bible Encyclopedia [13]

( מפתּה , maphtēaḥ , an "opener"; compare κλείς , kleı̄s , "that which shuts"): Made of wood, usually with nails which fitted into corresponding holes in the lock, or rather bolt (  Judges 3:25 ). Same is rendered "opening" in  1 Chronicles 9:27 . See House .

Figurative: Used figuratively for power, since the key was sometimes worn on the shoulder as a sign of official authority ( Isaiah 22-22 ). In the New Testament it is used several times thus figuratively: of Peter: "the keys of the kingdom of heaven" ( Matthew 16:19 ); of Christ, in Revelation, having the "keys of death and of Hades" ( Revelation 1:18 ), also having "the key of David" ( Revelation 3:7 ). An angel was given "the key of the pit of the abyss" ( Revelation 9:1;  Revelation 20:1 ). our Lord accused the teachers of the law of His day of taking away "the key of knowledge" from men, that is, locking the doors of truth against them ( Luke 11:52; compare  Matthew 23:13 ).

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [14]

is a common heraldic bearing in the insignia of sees and religious houses, particularly such as are under the patronage of St. Peter. Two keys in salire are frequent, and keys are sometimes interlaced or linked together at the Bows, i.e. rings. Keys indorsed are placed side by side, the wards away from each other.