Word Origin & History
prefix of negation, O.E. un-, from P.Gmc. *un- (cf. O.Fris., O.H.G., Ger. un-, Goth. un-, Du. on-), from PIE *n- (cf. Skt. a-, an- "not," Gk. a-, an-, O.Ir. an-, L. in-), a variant of PIE base *ne- "not" (cf. Avestan na, O.C.S., Lith. ne "not," L. ne "that not," Gk. ne- "not," O.Ir. ni, Corn. ny "not").
Freely and widely used since O.E. times in compounds with native and imported words, it disputes with Latin-derived cognate in
- the right to form the negation of certain words (indigestable/undigestable, etc.). Often euphemistic (e.g. untruth for "lie"). The most prolific of Eng. prefixes, it even is used to make words from phrases (e.g. uncalled-for, 1610; undreamed-of, 1636; uncome-at-able, 1694; unputdownable, 1947, of a book). As a prefix in telegram-ese to replace not
and save the cost of a word, it is first attested 1936.
prefix of reversal (e.g. unhand, undo, unbutton), O.E. on-, un-, from P.Gmc. *andi- (cf. O.S. ant-, O.N. and-, Du. ont-, O.H.G. ant-, Ger. ant-, Goth. and- "against"), from PIE *anti "facing opposite, near, in front of, before" (see ante