prefix 1 added to adjectives and participles and their derivative nouns and adverbs, meaning: a not: denoting the absence of a quality or state (unusable; uncalled-for; uneducated; unfailing; unofficially; unhappiness). b the reverse of, usu. with an implication of approval or disapproval, or with some other special connotation (unselfish; unsociable; unscientific). °Words formed in this way often have neutral counterparts in non- (see NON- 6) and counterparts in -in (see IN-(1)), e.g. unadvisable. 2 (less often) added to nouns, meaning 'a lack of' (unrest; untruth). °The number of words that can be formed with this prefix (and similarly with un-(2)) is potentially as large as the number of adjectives in use; consequently only a selection, being considered the most current or semantically noteworthy, can be given here.
[ OE f. Gmc, rel. to L in- ]