A [1] (also a) NOUN (pl. As or A's) 1) the first letter of the alphabet. 2) denoting the first, best, or most important in a set. 3) Music the sixth note of the diatonic scale of C major. 4) the human blood type (in the ABO system) containing the A antigen and lacking the B.
from A to B — Cf. ↑from A to B
from A to Z — Cf. ↑from A to Z
A [2] ABBREVIATION 1) ampere(s). 2) (Å) ångstrom(s). 3) (in showing goals or points conceded) against. 4) answer.

English terms dictionary. 2015.