Etymology: Middle English, from Old English; akin to Old High German un- un-, Latin in-, Greek a-, an-, Old English ne not — more at no
1. not ; in-, non- — in adjectives formed from adjectives <unambitious> <unskilled> or participles <undressed>, in nouns formed from nouns <unavailability>, and rarely in verbs formed from verbs <unbe> — sometimes in words that have a meaning that merely negates that of the base word and are thereby distinguished from words that prefix in- or a variant of it (as im-) to the same base word and have a meaning positively opposite to that of the base word <unartistic> <unmoral> 2. opposite of ; contrary to — in adjectives formed from adjectives <unconstitutional> <ungraceful> <unmannered> or participles <unbelieving> and in nouns formed from nouns <unrest> II. prefix Etymology: Middle English, from Old English un-, on-, alteration of and- against — more at ante- 1. do the opposite of ; reverse (a specified action) ; de- 1a, dis- 1a — in verbs formed from verbs <unbend> <undress> <unfold> 2. a. deprive of ; remove (a specified thing) from ; remove — in verbs formed from nouns <unfrock> <unsex> b. release from ; free from — in verbs formed from nouns <unhand> c. remove from ; extract from ; bring out of — in verbs formed from nouns <unbosom> d. cause to cease to be — in verbs formed from nouns <unman> 3. completely <unloose>
New Collegiate Dictionary. 2001.