the first letter of the English alphabet, a vowel.

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

something having the shape of an A.

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

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

from A to Z

from beginning to end; thoroughly; completely

He knows the Bible from A to Z.

not know from A to B

to know nothing; be ignorant.