Inflected forms: pl. a's or A's also as or As 1. The first letter of the modern English alphabet. 2. Any of the speech sounds represented by the letter a.3. The first in a series. 4. Something shaped like the letter A. 5.A The best or highest in quality or rank: grade A milk.6.Musica. The sixth tone in the scale of C major or the first tone in the relative minor scale. b. A key or scale in which A is the tonic. c. A written or printed note representing this tone. d. A string, key, or pipe tuned to the pitch of this tone. 7.A One of the four major blood groups in the ABO system. Individuals with this blood group have the A antigen on the surface of their red blood cells, and the anti-B antibody in their blood serum.
