"subsidiary consequence of an action, etc.," 1884, from side (adj.) + effect (n.). The specific medical use, with reference to drugs, is recorded by 1939.

"weak or unguarded aspect of a person or thing," c. 1600; see blind (adj.). As a verb, also blindside, "to hit from the blind side," attested from 1968, American English, in reference to U.S. football tackles.

1930, in reference to naval build-ups, from arms (see arm (n.2)) + race (n.1). First used in British English.

Latin legal term, "on the one side only," from ex "out of" (see ex-) + parte, ablative of pars "a part, piece, a division, a fraction, a side of the body" (from PIE root *pere- (2) "to grant, allot").

"financial losses, the debit side of an account," 1929, from the red ink traditionally used to indicate debits in accounts. Earlier, "cheap wine" (1919).

1917, from air (n.1) + force (n.); first attested with creation of the Royal Air Force. There was no United States Air Force until after World War II. The Air Corps was an arm of the U.S. Army. In 1942, the War Department reorganized it and renamed it Army Air Forces. The National Security Act of 1947 created the Department of the Air Force, headed by a Secretary of the Air Force, and the U.S.A.F.

mid-14c., also simply coat (mid-14c.); originally a tunic embroidered or painted with heraldic armorial bearings (worn over armor, etc); see coat (n.) + arm (n.2) and compare Old French cote a armer. Sense transferred in Middle English to the heraldic arms themselves. Hence turncoat, one who put his coat on inside-out to hide the badge of his loyalty (1550s).

powerful defoliant used by U.S. military in the Vietnam War, reported to have been used from 1961; so called from the color strip on the side of the container, which distinguished it from Agent Blue, Agent White, etc., other herbicides used by the U.S. military; see agent (n.). Banned from April 1970.

"one who advocates the contrary side," 1760, translating Latin advocatus diaboli, in the Catholic Church, a promoter of the faith and officer of the Sacred Congregation of Rites whose job it is to urge against the canonization of a candidate for sainthood. "[F]ar from being the whitewasher of the wicked, the [devil's advocate] is the blackener of the good." [Fowler]. Said to have been first employed in connection with the beatification of St. Lorenzo Giustiniani under Leo X (1513-21).

1726, in on the qui vive "on the alert," from French être sur le qui vive "be on the alert," from the phrase qui voulez-vous qui vive? sentinel's challenge, "whom do you wish to live?" In other words "(long) live who?" meaning "whose side are you on?" (The answer might be Vive la France, Vive le roi, etc.). From qui (from Latin qui "who") + vive, third person singular present subjunctive of vivre, from Latin vivere "to live" (see viva).