unreality (adj.)

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." Often euphemistic (such as untruth for "lie").

The most prolific of English prefixes, freely and widely used in Old English, where it forms more than 1,000 compounds. It underwent a mass extinction in early Middle English, but emerged with renewed vigor 16c. to form compounds with native and imported words. 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.

It also makes words from phrases (such as uncalled-for, c. 1600; undreamed-of, 1630s; uncome-at-able, 1690s; unputdownable, 1947, of a book; un-in-one-breath-utterable, Ben Jonson; etc., but the habit is not restricted to un-; such as put-up-able-with, 1812). As a prefix in telegramese to replace not and save the cost of a word, it is attested by 1936.

1540s, "quality of being real, objective reality," from French réalité and directly from Medieval Latin realitatem (nominative realitas), from Late Latin realis (see real (adj.)). Also compare realty, which was the older form of the word in the sense of "reality" (mid-15c.).

Meaning "real existence, what is real, the aggregate of all that is real" is from 1640s; that of "the real state (of something)" is from 1680s. Sometimes 17c.-18c. it also meant "sincerity." Reality-based is attested from 1960, in marriage counseling. Reality television is attested from 1991.