Origin and history of uncivil

late 14c., "relating to civil law or life; pertaining to the internal affairs of a state," from Old French civil "civil, relating to civil law" (13c.) and directly from Latin civilis "relating to a society, pertaining to public life, relating to the civic order, befitting a citizen," hence by extension "popular, affable, courteous;" alternative adjectival derivative of civis "townsman" (see city).

Meaning "not barbarous, civilized" is from 1550s. Specifically "relating to the commonwealth as secularly organized" (as opposed to military or ecclesiastical) by 1610s. Meaning "relating to the citizen in his relation to the commonwealth or to fellow citizens" also is from 1610s.

The word civil has about twelve different meanings; it is applied to all manner of objects, which are perfectly disparate. As opposed to criminal, it means all law not criminal. As opposed to ecclesiastical, it means all law not ecclesiastical: as opposed to military, it means all law not military, and so on. [John Austin, "Lectures on Jurisprudence," 1873]

The sense of "polite" was in classical Latin, but English did not pick up this nuance of the word until late 16c., and it has tended to descend in meaning to "meeting minimum standards of courtesy." "Courteous is thus more commonly said of superiors, civil of inferiors, since it implies or suggests the possibility of incivility or rudeness" [OED].

Civil, literally, applies to one who fulfills the duty of a citizen; It may mean simply not rude, or observant of the external courtesies of intercourse, or quick to do and say gratifying and complimentary things. ... Courteous, literally, expresses that style of politeness which belongs to courts: a courteous man is one who is gracefully respectful in his address and manner — one who exhibits a union of dignified complaisance and kindness. The word applies to all sincere kindness and attention. [Century Dictionary, 1895]

Civil case (as opposed to criminal) is recorded from 1610s. Civil liberty "natural liberty restrained by law only so far as is necessary for the public good" is by 1640s.

c. 1600, "barbarous, not reclaimed from savagery," from un- (1) "not" + past participle of civilize (v.). Uncivil in the same sense is recorded from 1550s but its sense has shifted to "impolite."

prefix of negation, Old English un-, from Proto-Germanic *un- (source also of Old Saxon, Old Frisian, Old High German, German un-, Gothic un-, Dutch on-), from PIE *n- (source of Sanskrit a-, an- "not," Greek a-, an-, Old Irish an-, Latin in-), combining form of PIE root *ne- "not."

The most prolific of English prefixes, freely and widely used in Old English, where it forms more than 1,000 compounds. It disputes with Latin-derived cognate in- (1) the right to form the negation of certain words (indigestable/undigestable, etc.), and though both might be deployed in cooperation to indicate shades of meaning (unfamous/infamous), typically they are not.

Often euphemistic (untruth for "a lie") or emphatic, if there is a sense already of divestment or releasing: unpeel " to peel;" unpick "pick (a lock) with burglars' tools;" unloose for "to loosen."

It also makes words from phrases, such as uncalled-for, c. 1600; undreamed-of, 1630s. Fuller (1661) has unbooklearned. A mid-15c. description of a legal will has unawaydoable; Ben Jonson has un-in-one-breath-utterable. The word uncome-at-able is attested by 1690s in Congreve, frowned at by Samuel Johnson in the 18th century and by Fowler in the 20th ("The word had doubtless, two or three centuries ago, a jolly daredevil hang-the-grammarians air about it ; that has long evaporated ; it serves no purpose that inaccessible does not ....").

But the practice continued; unlawlearned (Bentham, 1810), unlayholdable (1860); unputdownable, of a book, is by 1947; unpindownable, by 1966. Also compare put-up-able-with (1812). As a prefix in telegraphese, to replace not and save the cost of a word, it is attested by 1936.

With the variety of its possible use, and the need for negatives, the number of un- words that might be made in English is almost endless, and that some are used and some never is owing to the caprice of authors.

Dictionary editors noted this since 18c. but also padded the list. John Ash's "New and Complete Dictionary of the English Language" (1775) has many pages of one-line un- entries; among a dozen consecutive entries are unhaggled, unhaired, unhalooed, unhaltering (adj.), unhaltering (n.), which sorts of words OED (1989) notes were "obviously manufactured for the purpose" and some turn up in other texts only decades later, if at all. (Ash vindicated.)