Etymology
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break (v.)

Old English brecan "to divide solid matter violently into parts or fragments; to injure, violate (a promise, etc.), destroy, curtail; to break into, rush into; to burst forth, spring out; to subdue, tame" (class IV strong verb; past tense bræc, past participle brocen), from Proto-Germanic *brekanan (source also of Old Frisian breka, Dutch breken, Old High German brehhan, German brechen, Gothic brikan), from PIE root *bhreg- "to break."

Closely related to breach (n.), brake (n.1), brick (n.). The old past tense brake is obsolete or archaic; past participle is broken, but shortened form broke is attested from 14c. and was "exceedingly common" [OED] 17c.-18c.

Of bones in Old English. Formerly also of cloth, paper, etc. Meaning "escape by breaking an enclosure" is from late 14c. Intransitive sense "be or become separated into fragments or parts under action of some force" is from late 12c. Meaning "lessen, impair" is from late 15c. Meaning "make a first and partial disclosure" is from early 13c. Meaning "destroy continuity or completeness" in any way is from 1741. Of coins or bills, "to convert to smaller units of currency," by 1882. In reference to the heart from early 13c. (intransitive); to break (someone's) heart is late 14c.

Break bread "share food" (with) is from late 14c. To break ground is from 1670s as "to dig, plow," from 1709 in the figurative sense "begin to execute a plan." To break the ice "overcome the feeling of restraint in a new acquaintanceship" is from c. 1600, in reference to the "coldness" of encounters of strangers. Break wind first attested 1550s. To break (something) out (1890s) probably is an image from dock work, of freeing cargo before unloading it.

The ironic theatrical good luck formula break a leg (by 1948, said to be from at least 1920s) has parallels in German Hals- und Beinbruch "break your neck and leg," and Italian in bocca al lupo. Evidence of a highly superstitious craft (see Macbeth). According to Farmer & Henley, in 17c. the expression was used euphemistically, of a woman, "to have a bastard."

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break (n.)
c. 1300, "act of breaking, forcible disruption or separation," from break (v.). Sense in break of day "first appearance of light in the morning" is from 1580s; meaning "sudden, marked transition from one course, place, or state to another" is by 1725. Sense of "short interval between spells of work" (originally between lessons at school) is from 1861. Meaning "stroke of luck" is attested by 1911, probably an image from billiards (where the break that scatters the ordered balls and starts the game is attested from 1865). Meaning "stroke of mercy" is from 1914. Jazz musical sense of "improvised passage, solo" is from 1920s. Broadcasting sense is by 1941.
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down (adj.)

1560s, "directed downward," from down (adv.). Sense of "depressed mentally" is attested from c. 1600. Slang sense of "aware, wide awake" is attested from 1812. Computer crash sense is from 1965. Down-and-out "completely without resources" is from 1889, American English, from situation of a beaten prizefighter.

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down (n.3)

1710, "a downward movement," from down (adv.). Football sense of "an attempt to advance the ball" is by 1882.

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down (adv.)

"in a descending direction, from a higher to a lower place, degree, or condition," late Old English shortened form of Old English ofdune "downwards," originally of dune "off from (the) hill," from dune "from the hill," dative of dun "hill" (see down (n.2)). The "hill" word is general in Germanic, but this sense development is peculiar to English. As a preposition, "in a descending direction upon or along,"  from late 14c.

To be down on "express disapproval of" is by 1851. Down home is from 1828 as "in one's home region," as an adjective phrase meaning "unpretentious" by 1931, American English. Down the hatch as a toast is from 1931. Down to the wire is 1901, from horse-racing.

Down Under "Australia and New Zealand" attested from 1886; Down East "Maine" is from 1825; Down South "in the Southern states of the U.S." is attested by 1834. Down the road "in the future" is by 1964, U.S. colloquial. Down-to-earth "everyday, ordinary, realistic" is by 1932.

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down (v.)

1560s, "cause to go down," from down (adv.). Meaning "swallow hastily" is by 1860; football sense of "bring down (an opposing player) by tackling" is attested by 1887. Figurative sense of "defeat, get the better of" is by 1898. Related: Downed; downing.

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down (n.1)

"first feathers of a baby bird; soft covering of fowls under the feathers, the under-plumage of birds," used for stuffing pillows and feather-beds, mid-14c., from Old Norse dunn, which is of uncertain origin. Extended in Modern English to the soft hair of the human face and fine soft pubescence upon plants and some fruit.

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down (n.2)

"a hill of moderate elevation and more or less rounded outline," Old English dun "height, hill, moor," from Proto-Germanic *dunaz- (source also of Middle Dutch dunen "sandy hill," Dutch duin), "probably a pre-insular loan-word from Celtic" [Cambridge Dictionary of English Place-Names], in other words, borrowed at a very early period, before the Anglo-Saxon migration, perhaps from PIE root *dheue- "to close, finish, come full circle."

The more general meaning "elevated rolling grassland; high, rolling region not covered by forest" is from c. 1400. Specifically of certain natural pastureland districts of south and southeast England (the Downs) by mid-15c.

The non-English Germanic words tend to mean "dune, sand bank" (see dune), while the Celtic cognates tend to mean "hill, citadel" (compare Old Irish dun "hill, hill fort;" Welsh din "fortress, hill fort;" and second element in place names London, Verdun, etc.). German Düne, French dune, Italian, Spanish duna are said to be loan-words from Dutch.

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break-even (adj.)
also breakeven; usually with point, 1938, from the verbal phrase (1910); see break (v.) + even (adv.). The verbal phrase in the financial sense is recorded from 1914.
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jail-break (n.)
also jailbreak, "prison escape," 1828, from jail (n.) + break (n.). Verbal phrase to break jail is from 1735.
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