D defs.my
Entry 3 senses Webster, 1913

A B C

/(ā bē sē")/ · IPA
01 The first three letters of the alphabet, used for the whole alphabet.
  1. 1.
    The first three letters of the alphabet, used for the whole alphabet.
  2. 2.
    A primer for teaching the alphabet and first elements of reading.[Obs.]
  3. 3.
    The simplest rudiments of any subject; as, the A B C of finance.
Phrases & compounds
A B C book — a primer.