From BiblePortal Wikipedia

Hawker's Poor Man's Concordance And Dictionary [1]

One of the gracious offices of the Lord. All the persons of the Godhead have this blessed name and character applied to them in the Scriptures of truth; but it should seem to have a peculiar reference to the person of God the Father. Hence the Lord Jesus, with inexpressible sweetness, consigns the case of his church to his Father in the night before his sufferings and death. "Keep, Holy Father, (saith Jesus) through thine own name, those whom thou hast given me." ( John 17:12) So again the same or a similar request is made,  John 17:15 so also  Psalms 121:5. And the Holy Ghost, by Moses the man of God, when giving directions to Aaron to bless the people, appointed this form in reference to the Father. (See  Numbers 6:24 see also  Isaiah 27:3) And certainly there is a blessedness in the thought, that the church in Jesus is the continued object of the Father's love and care. And what an asylum do believers find in the view, that all the attributes of Jehovah are engaged for the security and comfort of his people. What the Lord said to Abraham is in effect said, and from the same cause, to all his seed: "Fear not, Abraham, I am thy shield, and thine exceeding great reward." ( Genesis 15:1)

Webster's Dictionary [2]

(1): ( n.) One who has the care, custody, or superintendence of anything; as, the keeper of a park, a pound, of sheep, of a gate, etc.; the keeper of attached property; hence, one who saves from harm; a defender; a preserver.

(2): ( n.) One who remains or keeps in a place or position.

(3): ( n.) A ring, strap, clamp, or any device for holding an object in place; as: (a) The box on a door jamb into which the bolt of a lock protrudes, when shot. (b) A ring serving to keep another ring on the finger. (c) A loop near the buckle of a strap to receive the end of the strap.

(4): ( n.) A fruit that keeps well; as, the Roxbury Russet is a good keeper.

(5): ( n.) One who retains in custody; one who has the care of a prison and the charge of prisoners.

(6): ( n.) One who, or that which, keeps; one who, or that which, holds or has possession of anything.

Vine's Expository Dictionary of NT Words [3]

1: Φύλαξ (Strong'S #5441 — Noun Masculine — phulax — foo'-lax )

akin to A, No. 4, above, "a guard:" see Guard.

 Matthew 28:4

King James Dictionary [4]

KEE'PER, n. One who keeps one that holds or has possession of any thing.

1. One who retains in custody one who has the care of a prison and the custody of prisoners. 2. One who has the care of a park or other inclosure,or the custody of beasts as the keeper of a park, a pound, or of sheep. 3. One who has the care, custody or superintendence of any thing.

In Great Britain, the keeper of the great seal, is a lord by his office,and one of the privy council. All royal grants, commissions and charters pass through his hands. He is constituted lord-keeper by the delivery of the great seal. The keeper of the privy seal is also a lord by his office,and a member of the privy council.

Hastings' Dictionary of the New Testament [5]

See Guard.

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [6]

in its widest sense, corresponds to the Heb. שׁוֹמֵר , Shomer', Gr. Τηρῶν ; in a special sense to נוֹטֵר or נוֹצֵר , a Watchman, as often rendered; רוֹעֵה , is a Shepherd; while שִׂר , Φῦλαξ , is a Guard over prisoners. These words are of frequent occurrence, besides others in certain peculiar senses or combinations, the meaning being clear from the connection.