ack

1939, representing A.A., the military abbreviation for anti-aircraft (see ack).

word used for the letter -t- in radio communication, 1898. Compare ack (-a-), emma (-m-).

fem. proper name, from German Emma, from Erma, contraction of Ermentrude or some similar name. With lower-case -e-, as British telephone and radio enunciation of -m- (to avoid confusion with -n-), attested by 1891, common in British soldier's jargon in World War I, for example ack emma "a.m.," pip emma "p.m." Compare ack (-a-), toc (-t-).