un

from The Century Dictionary.

• noun An inseparable prefix of verbs (generally transitive), meaning ‘back,’ and denoting the reversal or annulment of the action of the simple verb: as, undo, unlearn, unlock, unmake, etc.
• noun An in- separable prefix, meaning ‘not.’ It is prefixed to adjectives (including participles) and to adverbs, to express simply the negative, as unable, unfair, untrue, unwise, etc., unbending, unyielding, undoubting, unchanging, unthinking, etc., unbent, undoubted, unchanged, etc., ‘not able,’ ‘not fair,’ etc. The adverbs or nouns derived from such adjectives or participles (as unfairly, unfainess, etc.) may be regarded as formed from the adjective in un-, with the adverbial or noun formative (⟨ unfair + -ly, unfair + -ness), or as formed from such derived forms by prefixing the negative (⟨ un- + fairly, un- + fairness, etc.).
• noun It is prefixed to some nouns to express the absence, incompleteness, or the contrary of what the noun expresses, as in unrest, untruth, unwisdom, undress. Before an adjective in -ing, un- is nearly equivalent to -less after a noun: unresting is nearly equivalent to restless, unchanging to changeless, etc. This negative may be prefixed to any adjective or participle whatever, whether of native or of foreign origin. It is equivalent to its cognate in- of Latin origin, an-, a- of Greek origin, and also to non-, sometimes to dis-, etc., of Latin origin (the Latin forms, in-, etc., being used chiefly before adjectives of Latin origin, but also before other adjectives): thus, uncomplete, incomplete, and potentially non-complete; unelastic, inelastic, non-elastic; unemphatic, non-emphatic, etc.; unreputable, disreputable, etc. As un- may be prefixed to any adjective or participle whatever, it is needless, and it would be impracticable, to include all such formations in the dictionary. In the following pages only such are entered and defined as have had a special development, are used in senses not merely reversing the original adjective, or are in Middle English or Anglo-Saxon use, and so form the basis of all the later compounds, or are for other reasons noteworthy. For the meaning and history of the other forms in un-, see the corresponding simple forms. Of the forms here entered the etymology is usually obvious, and it is therefore not expressly given, except in the older and the exceptional words; the history will be found under the simple form. See also un-.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun dialectal One.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an organization of independent states formed in 1945 to promote international peace and security