unanticipated (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.

1530s, "to cause to happen sooner," a back-formation from anticipation, or else from Latin anticipatus, past participle of anticipare "take (care of) ahead of time," literally "taking into possession beforehand," from anti, an old form of ante "before" (from PIE root *ant- "front, forehead," with derivatives meaning "in front of, before") + capere "to take" (from PIE root *kap- "to grasp").

Later "prevent or preclude by prior action" (c. 1600) and "be aware of (something) coming at a future time" (1640s). Used in the sense of "expect, look forward to" since 1749, but anticipate has an element of "prepare for, forestall" that, etymologically, should prevent its being used as a synonym for expect. Related: Anticipated; anticipating.