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Fausset's Bible Dictionary [1]

( Αlρηα ( Α - Α ), Greek): ( Αlερη ( א ), "chief," "guide," Hebrew.) The first letter, as Ομεgα ( Ω - Ω ) is the last, of the Greek alphabet. So Christ is the First and the Last, including all that comes between, the Author and Finisher of the visible and invisible, and of the spiritual creations ( Revelation 1:8;  Revelation 21:6;  Revelation 22:13;  Hebrews 12:2;  Isaiah 41:4;  Isaiah 44:6). As He made originally, so will He complete the whole. Alphabet comes from the first two Greek letters, Αlpha ( Α - Α ), Βeta ( Β - Β ) equating in Hebrew to 'Αleph ( א ), Βet[H] ( ב ).

The Moabite stone of Dibon, probably of the reign of Ahaziah, Ahab's son, who died 896 B.C., exhibits an alphabet so complete that at that early date it can have been no recent invention. It has been discovered as mason's marks on the foundation stones of Solomon's temple. Yet even it was not the earliest form of the Palestinian alphabet. The fine discrimination of sounds, implied in inventing an alphabet, could hardly be brought to perfection at once Rawlinson fixes the invention 15 centuries B.C.

The language of the Dibon stone, and the Hebrew of the Bible, most closely agree. Mesha's victories are recorded there in the same character, and even the same idiom, as in 2 Kings 3. In symbols of the early Christian church A and were often combined with the cross, or with Christ's monogram, e.g., on a tablet in the catacombs at Melos, of the early part of the second century. The rabbis (Jalkut Rubeni, fol. 17, 4, Sohoettgen, Hor. Heb., 1:1086) say, "Adam transgressed the whole law from Αleph ( א ) to Τau ( ת )" (the last Hebrew letter); so Christ fulfilled it from Αlpha ( Α - Α ) to Οmega ( Ω - Ω ) ( Matthew 3:15).

Wilson's Dictionary of Bible Types [2]

 Revelation 1:8 (a) In this passage our Lord Jesus Himself applies this name to Himself as He does also in verse  Revelation 1:11. In  Revelation 21:6, He again applies that name to Himself and also in chapter  Revelation 22:13. He wants us to remember and never forget that He is the beginning of all literature. There would be no such thing as education, or understanding, or learning, were it not that He gave man the ability to learn, and then unveiled to man's mind the multitude of matters which we call education. All information about creation has come from Him. Those who shut Him out of their lives and thinking are in darkness, or return to darkness. He is the author of the solar system and of all chemicals. He is the designer of the earth and the heavens. He originated the plan of salvation.

He is the author of every kind of life in the vegetable kingdom, the animal kingdom and the human kingdom. Christ Jesus is first, He is before all in every department of the universe. As Alpha is the first letter of the Greek alphabet, so Christ is the first cause of everything that exists.

Smith's Bible Dictionary [3]

Alpha. Alpha, the first letter of the Greek alphabet. With Omega, the last letter, it is used in the Old Testament and in the New to express the eternity of God, as including both the beginning and the end.  Revelation 1:8;  Revelation 1:11;  Revelation 21:6;  Revelation 22:13;  Isaiah 41:4;  Isaiah 44:6.

Hence, these letters became a favorite symbol of the eternal divinity of our Lord, and were used for this purpose in connection with the cross, or the monogram of Christ (that is, the first two letters, Ch, and r, of Christ's name in Greek). Both Greeks and Hebrews employed the letters of the alphabet as numerals.

Hawker's Poor Man's Concordance And Dictionary [4]

We meet with this word,  Revelation 1:8; Rev 1:11. and in two other chapters of the Revelations. It is the first letter in the Greek alphabet. And the Lord Jesus, in having graciously condescended to call himself by this name, hath made it very precious to the believer. Jesus is, indeed, the Alpha and Omega, the first and the last, the Author and Finisher of salvation, It should seem that the Lord intended by this name, and adding to it Omega also, to imply the comprehensiveness of his nature, and being, both the first and the last, to intimate his eternity. (See  Isaiah 43:10)

See A

See Aleph

People's Dictionary of the Bible [5]

Alpha ( Ăl'Phah ). The first letter of the Greek alphabet, corresponding to Aleph, the first Hebrew letter. These letters were used as numerals. Alpha therefore denotes one, the first. And, as Omega is the last Greek letter, our Lord calls himself Alpha and Omega, the first and the last, implying his divine eternity.  Revelation 1:8;  Revelation 1:11;  Revelation 21:6;  Revelation 22:13; comp.  Isaiah 44:6.

Morrish Bible Dictionary [6]

The first letter of the Greek Alphabet, and which also signifies the numeral 1. A title or character of God and of Christ, which points to His eternity as 'the beginning,' 'the first,' the I AM.  Revelation 1:8;  Revelation 21:6;  Revelation 22:13 . "I am Alpha and Omega, the beginning and the end," or "the first and the last;" which is similar to a passage in  Isaiah 41:4 : "I Jehovah, the first, and with the last; I am he."

Watson's Biblical & Theological Dictionary [7]

the first letter of the Greek alphabet; Omega being the last letter. Hence Alpha and Omega is a title which Christ appropriates to himself,  Revelation 1:8;  Revelation 21:6;  Revelation 22:13; as signifying the beginning and the end, the first and the last, and thus properly denoting his perfection and eternity.

King James Dictionary [8]

AL'PHA, n. Heb. an ox, a leader.

The first letter in the Greek alphabet, answering to A, and used to denote first or beginning.

I am Alpha and Omega.  Revelation 1 .

As a numeral, it stands for one. It was formerly used also to denote chief as, Plato was the Alpha of the wits.

Webster's Dictionary [9]

(n.) The first letter in the Greek alphabet, answering to A, and hence used to denote the beginning.

American Tract Society Bible Dictionary [10]

See the letter A .

Kitto's Popular Cyclopedia of Biblial Literature [11]

Al´pha (Α ), the first letter of the Greek alphabet, corresponding to the Hebrew Aleph. Both the Hebrews and the Greeks employed the letters of their alphabets as numerals, and A (Alpha or Aleph)therefore denoted one or the first. Hence our Lord says of himself, that he is Alpha and Omega, i.e.the first and the last, the beginning and the ending, as he himself explains it ( Revelation 1:8;  Revelation 1:11;  Revelation 21:6;  Revelation 22:13).