un- (1) — ODE

un-1 /ʌn

▸ prefix

1 (added to adjectives, participles, and their derivatives) denoting the absence of a quality or state; not:

unabashed

unacademic

unrepeatable.

▪ the reverse of (usually with an implication of approval or disapproval, or with another special connotation):

unselfish

unprepossessing

unworldly.

2 (added to nouns) a lack of:

unrest

untruth.

The prefixes un- and non- both mean ‘not’, but there is often a distinction in terms of emphasis. un- tends to be stronger and less neutral than non-: consider the differences between unacademic and non-academic, for example (‘his language was refreshingly unacademic’; ‘a non-academic life suits him’).

– ORIGIN Old English un-, of Germanic origin; from an Indo-European root shared by Latin in- and Greek a-.