Etymology
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quarters (n.)

"military dwelling place," 1590s, from quarter (n.1) in sense of "portion of a town." As "part of an American plantation where the slaves live," from 1724. The military sense seems to be also the source of quartermaster and it might be behind the phrase give quarter "spare from immediate death" (1610s, often in the negative), on the notion of "provide a prisoner with shelter;" see quarter (n.2).

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military (n.)

"soldiers generally," 1757, from military (adj.); commonly only with the definite article. Earlier, "a military man" (1736).

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military (adj.)

mid-15c., militari, "pertaining to or befitting soldiers; used, done, or brought about by soldiers," from Old French militaire (14c.) and directly from Latin militaris "of soldiers or war, of military service, warlike," from miles (genitive militis) "soldier," a word of unknown origin.

Perhaps ultimately from Etruscan, or else meaning "one who marches in a troop," and thus connected to Sanskrit melah "assembly," Greek homilos "assembled crowd, throng." De Vaan writes, "It is tempting to connect mīlia [pl.] 'thousand(s)', hence *mīli-it- 'who goes with/by the thousand' ...." Related: Militarily. Old English had militisc, from Latin.

Military police is from 1827. Military age, at which one becomes liable to military service, is by 1737. Military-industrial complex was coined 1961 in the farewell speech of U.S. president Dwight D. Eisenhower.

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headquarters (n.)
"residence of a military commander," 1640s, from head (adj.) + quarters. Headquarter as a verb is recorded from 1838 (in Headquartered).
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cantonment (n.)
1756, "military quarters, part of a town assigned to a particular regiment," from French cantonnement, from cantonner "to divide into cantons" (14c.), from canton "angle, corner" (see canton). Meaning "action of quartering troops" is from 1757.
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post (n.2)

"station when on duty, a fixed position or place," 1590s, from French poste "place where one is stationed," also, "station for post horses" (16c.), from Italian posto "post, station," from Vulgar Latin *postum, from Latin positum, neuter past participle of ponere "to place, to put" (see position (n.)). Earliest sense in English was military; the meaning "job, position, position" is attested by 1690s. The military meaning "fort, permanent quarters for troops" is by 1703.

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taps (n.)
U.S. military signal for lights out in soldiers' quarters (played 15 minutes after tattoo), 1824, from tap (v.), on the notion of drum taps (it originally was played on a drum, later on a bugle). As a soldier's last farewell, played over his grave, it may date to the American Civil War. The tune was revised several times in mid-19c.
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camper (n.)
1630s, "soldier," agent noun from camp (v.). Meaning "attendee at a camp meeting" is from 1806; meaning "one who sleeps in temporary quarters outdoors" is from 1856; that of "motor vehicle with sleeping quarters" is from 1960. Extended use of happy camper is from c. 1987.
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POSSLQ 
1979, acronym from person of opposite sex sharing living quarters; it never was an official category.
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harbor (v.)
Old English herebeorgian "take up quarters, lodge, shelter oneself" (cognate with Old Norse herbergja, Old High German heribergon, Middle Dutch herbergen), verbal formation from here-beorg "lodgings, quarters" (see harbor (n.)). Meaning "give shelter to, protect" is from mid-14c. Figuratively, of thoughts, etc., from late 14c. Related: Harbored; harboring.
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