Pronunciation: (un), [key]
one: young uns; He's a bad un. Also,'un.
a prefix meaning “not,” freely used as an English formative, giving negative or opposite force in adjectives and their derivative adverbs and nouns (unfair; unfairly; unfairness; unfelt; unseen; unfitting; unformed; unheard-of; un-get-at-able), and less freely used in certain other nouns (unrest; unemployment).
a prefix freely used in English to form verbs expressing a reversal of some action or state, or removal, deprivation, release, etc. (unbend; uncork; unfasten; etc.), or to intensify the force of a verb already having such a meaning (unloose).
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.