Etymology
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cui bono 

a Latin phrase from Cicero. It means "to whom for a benefit," or "who profits by it?" not "to what good purpose? for what use or end?" as is sometimes said. From cui "to? for whom?," an old form preserved here in the dative form of the interrogative pronoun quis "who?" (from PIE root *kwo-, stem of relative and interrogative pronouns) + bono "good" (see bene-).

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lame duck (n.)

1761, "any disabled person or thing;" especially Stock Exchange slang for "defaulter."

A lame duck is a man who cannot pay his differences, and is said to waddle off. [Thomas Love Peacock, "Gryll Grange," 1861]

Sometimes also in naval use for "an old, slow ship." Modern sense of "public official serving out term after an election" is recorded by 1863, American English. The quote attributed to President Lincoln ("[A] senator or representative out of business is a sort of lame duck. He has to be provided for") is from an anecdote of 1878.

It is well known to everybody who knows anything of its history, that this court [Court of Claims] was made a sort of retreat for lame duck politicians that got wounded and had to retreat before the face of popular condemnation. That is just exactly what it was for, a safe retreat for lame ducks; and it was so filled up; (etc.) [Sen. John P. Hale, New Hampshire, Congressional Globe, Jan. 12, 1863, p.271]
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aqua fortis (n.)
also aquafortis, old commercial name for "diluted nitric acid," c. 1600, Latin, literally "strong water;" see aqua- + fort. So called for its power of dissolving metals (copper, silver) which are unaffected by other agents.
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VE Day (n.)
initialism (acronym) for Victory in Europe, from September 1944 (see victory).
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camera obscura (n.)
1725, "a darkened room;" c. 1730, "a device for project pictures;" see camera.
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pret a porter (adj.)

denoting clothes sold in standard sizes, 1957, from French prêt à porter, "ready-to-wear." For pret, see presto. Porter is literally "to carry," from Latin portare "to carry" (from PIE root *per- (2) "to lead, pass over"). For a similar sense evolution, compare German kleider tragen.

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drawing room (n.)

"room appropriated for the reception of company," 1640s, short for withdrawing room (16c.; see withdraw), into which ladies would retire after dinner. Earlier in the sense of "private room" as draw-chamber (mid-15c.); drawyng chaumber (early 15c.).

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post restante 

direction on mail that it be held at that post office until called for, French, literally "remaining post." Hence, place in a post office where letters so addressed are kept until the recipients call for them.

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boot camp (n.)
"training station for recruits," by 1941, U.S. Marines slang, said to be from boot (n.1) as slang for "recruit," which is attested by 1915 and supposedly dates from the Spanish-American War and is a synecdoche from boots "leggings worn by U.S. sailors."
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feng shui (n.)
also feng-shui, fung-shui, 1797, from Chinese, from feng "wind" + shui "water." A system of spiritual influences in natural landscapes and a means of regulating them; "A kind of geomancy practiced by the Chinese for determining the luckiness or unluckiness of sites for graves, houses, cities, etc." [Century Dictionary].
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