A, a [ey]
noun, plural 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.


  1. from A to Z, from beginning to end; thoroughly; completely: He knows the Bible from A to Z.
  2. not know from A to B, to know nothing; be ignorant.