Etymology
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Iron Age 
1590s, originally, as in Greek and Roman mythology, the last and worst age of the world; the archaeological sense of "period in which humans used iron tools and weapons" is from 1866 (earlier in this sense iron period, 1847).
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life of Riley (n.)

"life at ease," by 1902 (as Reilly), popularized in U.S. during World War I; it seems to have been military slang initially, sometimes said to trace to various songs but none of that title has been found.

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Wall Street (n.)
"U.S. financial world," 1836, from street in New York City that is home to many investment firms and stock traders, as well as NYSE. The street so called because it ran along the interior of the defensive wall of the old Dutch colonial town.
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black market (n.)
"unauthorized dealing in restricted or rationed commodities," 1931, from black (adj.), probably suggesting "dark, invisible" or "shady, improper" + market (n.). As an adjective by 1935. It exploded in popularity with the coming of World War II rationing.
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piss off (v.)

1958, intransitive, "go away," chiefly British; the transitive meaning "annoy (someone)" is by 1968, chiefly U.S.; from piss (v.) + off (adv.). Pissed off "angry, fed up" is attested by 1946 (Partridge says 1937); said to have been used in the military in World War II; in common use from 1970s.

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go west (v.)
19c. British idiom for "die, be killed" (popularized during World War I), "probably from thieves' slang, wherein to go west meant to go to Tyburn, hence to be hanged, though the phrase has indubitably been influenced by the setting of the sun in the west" [Partridge]. Compare go south.
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yellow journalism 
"sensational chauvinism in the media," 1898, American English, from newspaper agitation for war with Spain; originally "publicity stunt use of colored ink" (1895) in reference to the popular Yellow Kid" character (his clothes were yellow) in Richard Outcault's comic strip "Shantytown" in the "New York World."
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care package (n.)
1945, originally CARE package, supplies sent out by "Cooperative for American Remittances to Europe," established 1945 by U.S. private charities to coordinate delivery of aid packages to displaced persons in Europe after World War II and obviously named for the sake of the acronym. Name reupholstered late 1940s to "Cooperative for Assistance and Relief Everywhere," to reflect its expanded mission.
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kitchen sink (n.)

sink to wash food, dishes, etc., 1824. Phrase everything but (or and) the kitchen sink is attested from 1944, from World War II armed forces slang, in reference to intense bombardment.

Out for blood, our Navy throws everything but the kitchen sink at Jap vessels, warships and transports alike. [Shell fuel advertisement, Life magazine, Jan. 24, 1944]

Earlier was everything but the kitchen stove (1919).

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air force (n.)
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.
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