Etymology
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let-up (n.)
"cessation, restraint, relaxation, intermission," 1837, from verbal phrase let up "cease, stop" (1787). In Old English the phrase meant "to put ashore" (let out meant "put to sea"). Bartlett (1848) says the noun is "an expression borrowed from pugilists."
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smash-up (n.)
"collision," 1841, from verbal phrase; see smash (v.) + up (adv.).
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touch-up (n.)
"act of improvement requiring modest effort," 1872, from verbal phrase touch up "improve or finish (as a painting or drawing) with light strokes" (1715), from touch (v.) + up (adv.).
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warm-up (n.)
"act or practice of exercising or practicing before an activity," 1915; earlier in literal sense, "a heating" (of something), 1878, from verbal phrase warm up, which is from 1868 in the sense "exercise before an activity." Earlier in reference to heating food (1848), and earliest (c. 1400), figuratively, of persons. In reference to appliances, motors, etc., attested from 1947.
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wind-up (n.)
1570s, "conclusion or final adjustment and settlement of some matter," from verbal phrase wind up (see wind (v.1)). Baseball pitching sense attested from 1906.
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wrap-up (n.)
"summary," 1947, from the verbal phrase (see wrap (v.)).
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flare-up (n.)

"a sudden burst," 1827 of an argument; 1858 of light, from verbal phrase; see flare (v.) + up (adv.). It seems to have had some vogue as a street expression in London in the 1830s.

Flare up! flare up! is all the cry, in every square and street —
No other sound salutes your ear, whoe'er you chance to meet
Where'er you ride, or walk, or sit, or breakfast, dine, or sup,
They welcome you or quiz you with "Flare up, my boy! flare up!"
[Fraser's Magazine, April 1834]
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crack-up (n.)

1926, in reference to airplane crashes; 1936, "disintegration under stress, mental collapse" [Fitzgerald]; from the verbal phrase, from crack (v.) + up (adv.). The verbal phrase in the meaning "to break up laughing" is by 1967, transitive and intransitive. Its earliest sense was "to praise extravagantly" (as in not all it's cracked up to be).

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kickboxing (n.)
also kick-boxing, 1968, from kick (n.) + boxing (n.). Related: Kickbox (v.); kickboxer (1978).
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