1889, civvies, short for civilian clothes (see civilian); in reference to civilian clothes of military men.
"ordinary dress of civil life" (as opposed to military uniform), 1822; in reference to police detectives, it is attested from 1842. Also plainclothes.
"action of disarming," by 1795; see noun of action from disarm. Especially in reference to reduction of military and naval forces from a war to a peace footing.
also mechanised, in the military sense of "equipped with or using mechanical vehicles and weapons," 1926, past-participle adjective from mechanize (v.).
of a college or university student, "focus (one's) studies," 1910, American English, from major (n.) in sense of "subject of specialization" (by 1890). Related: Majored; majoring. Earlier as a verb, in Scottish, "to prance about, or walk backwards and forwards with a military air and step" [Jamieson, 1825] a sense derived from the military major.