orig military, now dated. adverb orig military, now dated. adverb 1: Ante meridiem; in the morning. (1898 —) . D.L.Sayers Some damned thing at the Yard, I suppose. At three ack emma! (1927).noun 2: (in the RAF) An air mechanic. (1930 —) . Compare pip emma at pip2noun.
[From the former military communications code-names for the letters a and m.]