late 14c., "a small private room for study or prayer," from Old French closet "small enclosure, private room," diminutive of clos "enclosure," from Latin clausum "closed space, enclosure, confinement," from neuter past participle of claudere "to shut" (see close (v.)).

In Matthew vi.6 it renders Latin cubiculum "bedchamber, bedroom," Greek tamieion "chamber, inner chamber, secret room." Modern sense of "small side-room for storage" is first recorded 1610s.

The adjective is from 1680s, "private, done in seclusion;" from 1782 as "fitted only for scholarly seclusion, not adopted to the conditions of practical life." The meaning "secret, not public, unknown" is recorded from 1952, first of alcoholism but by 1970s used principally of homosexuality; the phrase come out of the closet "admit something openly" is first recorded 1963, and lent a new meaning to the word out.

late 14c., "action of going out, an issuing forth;" mid-15c., "act of putting or driving out, expulsion, ejection;" verbal noun from out (v.). Original senses are now obsolete. The meaning "an excursion, a pleasure-trip" is from 1821.

"put out, extinguish," especially in outen the light, 1916, American English dialectal; see out (adv.) + -en (1). An idiom in Pennsylvania German. In English, out (v.) "to put out" is attested from c. 1500.

Middle English aboute, from Old English abutan (adv., prep.), earlier onbutan "on the outside of; around the circumference of, enveloping; in the vicinity of, near; hither and thither, from place to place," also "with a rotating or spinning motion," in late Old English "near in time, number, degree, etc., approximately;" a compound or contraction of on (see on; also see a- (1)) + be "by" (see by) + utan "outside," from ut (see out (adv.)).

By c. 1300 it had developed senses of "around, in a circular course, round and round; on every side, so as to surround; in every direction;" also "engaged in" (Wist ye not that I must be about my Father's business?), and gradually it forced out Old English ymbe, ymbutan (from PIE root *ambhi- "around") in the sense "round about, in the neighborhood of."

From mid-13c. as "in the matter, in connection with." From early 14c. as "in partial rotation, so as to face in a different direction." From late 14c. as "near at hand, about one's person." "In a circuitous course," hence "on the move" (late 13c.), and in Middle English "be about to do, be busy in preparation for," hence its use as a future participle in (to be) about to "in readiness, intending." Abouts (late 14c.), with adverbial genitive, still found in hereabouts, etc., probably is a northern dialectal form.

To bring about "cause or affect" and to come about "happen" are from late 14c. About face as a military command (short for right about face) is first attested 1861, American English.

also bail-out 1945, in aviation, from the verbal phrase in reference to pilots; see bail (v.1) + out (adv.). As "federal help for private business in trouble," from 1968; it is unclear which sense of bail is meant there.

also black-out, 1908 in the theatrical sense of a darkened stage, from the verbal phrase; see black (v.) + out (adv.). The figurative sense of "loss of memory" is by 1934 (verb and noun); as "a dousing of lights as an air raid precaution," it is recorded from 1935. The verbal phrase black out, in reference to using black ink to cover printed or written matter deemed objectionable, is attested from 1888.

also blowout, 1825, American English colloquial, "outburst, brouhaha" (what in modern vernacular would be called a blow-up), from the verbal phrase, in reference to pressure in a steam engine, etc., from blow (v.1) + out (adv.). The meaning "abundant feast" is recorded from 1824; that of "a bursting of an automobile tire" is from 1908.

also break-out, "act of issuing or springing out," 1820, from the verbal phrase, "issue forth, arise, spring up;" see break (v.) + out (adv.). The verbal phrase goes back to Old English ut brecan, utabrecan. Transitive sense is attested from 1610s.

also burnout, "drug user," by 1972, slang, from the verbal phrase, which is attested from 1590s in the sense "burn until fuel is exhausted;" see burn (v.) + out (adv.). The immediate source is perhaps the use of the phrase in reference to electrical circuits, "fuse or cease to function from overload" (1931). Also compare burnt out "extinct after entire consumption of fuel" (1837). The meaning "mental exhaustion from continuous effort" is from 1975.

Old English butan, buton "unless; with the exception of; without, outside," from West Germanic *be-utan, a compound of *be- "by" (see by) + *utana "out, outside; from without," from ut "out" (see out (adv.)). Not used as a conjunction until late Old English, "on the contrary." Senses attested in early Middle English include "however, yet; no more than." As an introductory expression, early 13c. As a noun, "an objection, an exception" from late 14c.

Som man preiseth his neighebore by a wikked entente, foralwey he maketh a 'but' at the laste ende, that is digne of moore blame than worth is al the preisynge. [Chaucer, "Parson's Tale"]