A, a

/ay/, n., pl. A's or As, a's or as.

1. the first letter of the English alphabet, a vowel.

2. any spoken sound represented by the letter A or a, as in bake, hat, father, or small.

3. something having the shape of an A.

4. a written or printed representation of the letter A or a.

5. a device, as a printer's type, for reproducing the letter A or a.

6. from A to Z, from beginning to end; thoroughly; completely: He knows the Bible from A to Z.

7. not know from A to B, to know nothing; be ignorant.