1) first letter of Greek alphabet
2) Christ is the Alpha to indicate that he is the beginning and the end
Part of Speech: letter
Citing in TDNT: 1:1,*
Of Hebrew origin; the first letter of the alphabet: figuratively only (from its use as a numeral) the first. Often used (usually "an", before a vowel) also in composition (as a contraction from G427) in the sense of privation; so in many words beginning with this letter; occasionally in the sense of union (as a contraction of G260): - Alpha.
These two sites give similar information, with the definition from several dictionaries and statistics on the use of the word.
Perseus Digital Library
University of Chicago's Logion lexicon
Thayer's dictionary plus other information.
From this site's dictionary (in Italian)
Click on the first column to search for that word as a form of the root Ἄλφα; click on the second column to search for that grammatical form of the root Ἄλφα; click on the third column to search for that word and grammatical form; click on the total to search for the root Ἄλφα.