also a-b-c, late 13c. (spelled abece) from the first three letters of it taken as a word (compare alphabet, abecedary, Old French abecé, abecedé "alphabet," 13c.). The sense of "rudiments or fundamentals (of a subject)" is from late 14c. As a shortening of American Broadcasting Company from 1944 (in a Billboard magazine headline), earlier of Australian Broadcasting Corporation (1931). Related: ABCs.