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.
[uh
n] 
,