Etymology
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pipe dream (n.)

the sort of improbable fantasy one has while smoking opium, 1870, from pipe (n.1) in the smoking sense + dream (n.). Old English pipdream meant "piping," from dream in the sense of "music."

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black box (n.)

1947, RAF slang for "navigational instruments;" later extended to any sort of apparatus that operates in a sealed container. Especially of flight recorders from c. 1964.

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Brown Shirt (n.)

generic term for "Nazi, fascist," especially of the thuggish sort, 1934, originally (1922) in reference to the German Sturmabteilung ("Storm Detachment"), the Nazi party militia founded 1921; they were called Brown Shirts in English because of their uniforms.

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Deo volente 

1767, Latin, "God willing," that is, "if nothing prevents it, if it is meant to be," a sort of verbal knock on wood, from ablative of Deus "God" (see Zeus) + ablative of volentem, present participle of velle "to wish, will" (see will (v.)). Often abbreviated D.V.

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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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seven-year itch (n.)

1899, American English, some sort of skin condition (sometimes identified with poison ivy infection) that either lasts seven years or returns every seven years. Jocular use for "urge to stray from marital fidelity" is attested from 1952, as the title of the Broadway play (made into a film, 1955) by George Axelrod (1922-2003), in which the lead male character reads an article describing the high number of men have extra-marital affairs after seven years of marriage.

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hat trick (n.)

in the sports sense, 1879, originally in cricket, "taking three wickets on three consecutive deliveries;" extended to other sports c. 1909, especially ice hockey ("In an earlier contest we had handed Army a 6-2 defeat at West Point as Billy Sloane performed hockey's spectacular 'hat trick' by scoring three goals" ["Princeton Alumni Weekly," Feb. 10, 1941]). So called allegedly because it entitled the bowler to receive a hat from his club commemorating the feat (or entitled him to pass the hat for a cash collection), but the term probably has been influenced by the image of a conjurer pulling objects from his hat (an act attested by 1876). The term was used earlier for a different sort of magic trick:

Place a glass of liquor on the table, put a hat over it, and say, "I will engage to drink every drop of that liquor, and yet I'll not touch the hat." You then get under the table; and after giving three knocks, you make a noise with your mouth, as if you were swallowing the liquor. Then, getting from under the table, say "Now, gentlemen, be pleased to look." Some one, eager to see if you have drunk the liquor, will raise the hat; when you instantly take the glass and swallow the contents, saying, "Gentlemen I have fulfilled my promise: you are all witnesses that I did not touch the hat." ["Wit and Wisdom," London, 1860]
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