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).

Nearby words

  1. umtata,
  2. umu,
  3. umw,
  4. umwelt,
  5. un,
  6. un-american,
  7. un-british,
  8. un-english,
  9. una,
  10. una corda

Compare un-2.

Origin of un-

Middle English un-, on-, Old English; cognate with Dutch on-, Gothic, German un-, Old Norse ū-, ō-; akin to Latin in-, Greek an-, a-. See a-6, an-1, in-3

Synonym study

See in-3.



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).
Compare un-1.

Origin of un-

Middle English, Old English un-, on-; cognate with Gothic and-, Dutch ont-, German ent-; akin to Latin ante, Greek antí; cf. ante-, anti-

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for un-




(freely used with adjectives, participles, and their derivative adverbs and nouns: less frequently used with certain other nouns) not; contrary to; opposite ofuncertain; uncomplaining; unemotionally; untidiness; unbelief; unrest; untruth

Word Origin for un-

from Old English on-, un-; related to Gothic on-, German un-, Latin in-

prefix forming verbs and verbal derivatives

denoting reversal of an action or stateuncover; untangle
denoting removal from, release, or deprivationunharness; unman; unthrone

Word Origin for un-

from Old English un-, on-; related to Gothic and-, German ent-, Latin ante

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for un-
Online Etymology Dictionary, © 2010 Douglas Harper

Medicine definitions for un-




The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.