1. Not: unhappy.
2. Opposite of; contrary to: unrest.
[Middle English, from Old English; see ne in the Appendix of Indo-European roots.]
Usage Note: There are two prefixes spelled un- in English. One has the basic meaning "not" and attaches chiefly to adjectives (unable, unclean, unequal, unripe, unsafe) and participles used as adjectives (unfeeling, unflinching, unfinished, unsaid). Less frequently, it attaches to nouns (unbelief, unconcern, unrest). Sometimes the noun form of an adjective with the un- prefix has the prefix in-, as in inability, inequality, injustice, and instability. A few stems appear with both prefixes with distinctions of meaning. Inhuman means "brutal, monstrous," while unhuman means "not of human form, superhuman." · When used with adjectives, un- often has a sense distinct from that of non-. Non- picks out the set of things that are not in the category denoted by the stem to which it is attached, whereas un- picks out properties unlike those of the typical examples of the category. Thus nonmilitary personnel are those who are not members of the military, whereas someone who is unmilitary is unlike a typical soldier in dress, habits, or attitudes. · The other prefix un- is not related, despite its common origin in Old English. It forms verbs and expresses removal, reversal, or deprivation: undress, unravel, unnerve. This un- is in fact related to the Greek prefix anti-, "against, opposite, in return," which appears in English as the prefix anti-.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.