/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.