\A B C"\ ([=a] b[=e] s[=e]").
1. The first three letters of the alphabet, used for the
   whole alphabet.
2. A primer for teaching the alphabet and first elements of
   reading. [Obs.]
3. The simplest rudiments of any subject; as, the A B C of
   finance.
{A B C book}, a primer. --Shak.