Definition of: a, A

(ā) noun plural a's, A' or As, aes (āz)
1. The first letter of the English alphabet: from Phoenician aleph, through the Hebrew aleph, Greek alpha, and Roman A.
2. Any sound of the letter ‘a. See ALPHABET.
—symbol
1. Primacy in class or order: grade A beef.
2. A substitute for the numeral l: section A.
3. Music a One of a series of tones, the sixth in the natural diatonic scale of C, or the first note in the related minor scale. b A standard for tuning instruments: the pitch of this tone. c The written note representing this tone. d The scale built upon A.
3. Chem. Argon (symbol A).