"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).
Old English carian, cearian "be anxious or solicitous; grieve; feel concern or interest," from Proto-Germanic *karo- "lament," hence "grief, care" (source also of Old Saxon karon "to lament, to care, to sorrow, complain," Old High German charon "complain, lament," Gothic karon "be anxious"), said to be from PIE root *gar- "cry out, call, scream" (source also of Irish gairm "shout, cry, call;" see garrulous).
If so, the prehistoric sense development is from "cry" to "lamentation" to "grief." A different sense evolution is represented in related Dutch karig "scanty, frugal," German karg "stingy, scanty." It is not considered to be related to Latin cura. Positive senses, such as "have an inclination" (1550s); "have fondness for" (1520s) seem to have developed later as mirrors to the earlier negative ones.
To not care as a negative dismissal is attested from mid-13c. Phrase couldn't care less is from 1946; could care less in the same sense (with an understood negative) is from 1955. Care also has figured since 1580s in many "similies of indifference" in the form don't care a _____, with the blank filled by fig, pin, button, cent, straw, rush, point, farthing, snap, etc., etc. Related: Cared; caring.
1540s, "having a conscience;" 1580s, of actions, "consonant with right or duty;" 1640s, of persons, "governed by conscience." It and conscioned "appear to be popular formations from conscion, taken as a singular of conscien-ce" by misapprehension of the "s" sound as a plural inflection [OED]. See conscience. Related: Conscionably. Obsolete from early 18c. but fossilized in its negative, unconscionable.
"solemn renunciation," mid-15c., originally of heresy or idolatry, later of renunciations of oaths generally, from Latin abiurationem (nominative abiuratio) "a denying on oath," noun of action from past-participle stem of abiurare "deny on oath," from ab "off, away from" (see ab-) + iurare "to swear," from ius (genitive iuris) "law" (see jurist). Related: Abjuratory. The oath of abjuration is "the negative part of the oath of allegiance" [Century Dictionary].
c. 1300, "unbelieving," from faith + -less. Meaning "insincere, deceptive" is mid-14c. Related: Faithlessly; faithlessness.
Unfaithful ... especially means a lack of fidelity to trust or duty, a failure to perform what is due, however much may be implied in that. Faithless is negative in form, but positive in sense; the faithless man does something which is a breach of faith; the sleeping sentinel is unfaithful; the deserter is faithless. [Century Dictionary, 1895]
"ineffectual or hapless person," 1905, nebbich, from Yiddish (used as a Yiddish word in American English from 1890s), from a Slavic source akin to Czech neboh "poor, unfortunate," literally "un-endowed," from Proto-Slavic *ne-bogu-, with negative prefix (see un- (1)) + from PIE root *bhag- "to share out, apportion; to get a share." Also as an adjective.
