Online Etymology Dictionary

unlamented (adj.): 1590s, from un- (1) "not" + past participle of lament (v.).
unlatch (v.): 1640s, from un- (2) "reverse, opposite of" + latch (v.).
unlawful (adj.): "contrary to law, illegal," c. 1300, from un- (1) "not" + lawful. Unlawful assembly is recorded in statutes from late 15c. Related: Unlawfully. Old English had a noun unlagu ("unlaw") "illegal action, abuse of law."
unleaded (adj.): 1610s, "having no lead," from un- (1) "not" + leaded (see lead (v.2)). In reference to gasoline, from 1965. In reference to printing, from 1902.
unlearn (v.): mid-15c., from un- (2) "reverse, opposite of" + learn (v.).
unlearned (adj.): c. 1400, "ignorant," from un- (1) "not" + learned (adj.). From 1530s as "not acquired by learning," from past participle of learn (v.). Old English had unlæred.
unleash (v.): 1670s, from un- (2) "reverse, opposite of" + leash (v.). Related: Unleashed; unleashing.
unleavened (adj.): 1520s, from un- (1) "not" + past participle of leaven (v.).
unless (conj.): mid-15c., earlier onlesse, from (not) on lesse (than) "(not) on a less compelling condition (than);" see less. The first syllable originally on, but the negative connotation and the lack of stress changed it to un-. "Except could once be used as a synonym for unless, but the words have now drawn entirely apart" [Century Dictionary].
unlettered (adj.): mid-14c., "not possessed of book-learning," from un- (1) "not" + lettered. An Englished form of illiterate. Similar formation in Middle Dutch ongelettert.
unlicensed (adj.): 1630s, from un- (1) "not" + past participle of license (v.).
unlike (adj.): c. 1200, "not resembling," from un- (1) "not" + like (adj.). Similar formation in Old English ungelic, Old Frisian unlik, Old Norse ulikr, Middle Danish ulige, German ungleich.
unlike (adv.): c. 1300, "unevenly," from un- (1) "not" + like (adv.) (see like (adj.)). From 1590s as "in a manner differing."
unlikely (adj.): late 14c., "not likely to occur," from un- (1) "not" + likely (adj.). Similar formation in Old Norse ulikligr, Middle Danish uligelig. Meaning "not likely to be true" is recorded from 1590s. Related: Unlikeliness; unlikelihood.
unlikely (adv.): mid-15c., "improbably," from un- (1) "not" + likely (adv.) (see likely (adj.)).
unlimber (v.): 1760, "to free (a gun) from its limber," usually for the purpose of bringing it into action, from un- (2) "opposite of" + limber "attach a gun to its limber" (see limber (n.)). Figurative sense is attested from 1864. Related: Unlimbered; unlimbering.
unlimited (adj.): mid-15c., from un- (1) "not" + past participle of limit (v.).
unlink (v.): c. 1600, from un- (2) "reverse, opposite of" + past participle of link (v.). Related: Unlinked; unlinking.
unlisted (adj.): 1640s, from un- (1) "not" + past participle of list (v.3). In reference to stocks, attested from 1905; of phone numbers, from 1937 (American English).
unlivable (adj.): 1834, "incapable of being lived in," from un- (1) "not" + livable.
unload (v.): 1520s, in reference to cargo, from un- (2) + load (v.). Figurative sense (in reference to feelings, etc.) is recorded from 1590s. Used in reference to sales of stocks by 1870, hence U.S. colloquial sense "dispose of property the holding of which is risky" (1881). Related: Unloaded; unloading.
unlock (v.): c. 1400, from un- (2) "reverse, opposite of" + lock (v.). Figurative sense is attested from 1530s. Old English had unlucan "to unlock, open." Related: Unlocked; unlocking.
unlooked (adj.): c. 1300, "neglected," from un- (1) "not" + past participle of look (v.). With for, "unexpected," attested from 1530s.
unloose (v.): mid-14c., "relax;" late 14c., "to set free," from un- (2), used here emphatically, + loose (v.). Old English had unliesan "unloose, set free." Related: Unloosed; unloosing.
unloved (adj.): late 14c., from un- (1) "not" + past participle of love (v.). A verb, unlove (with un- (2)) is attested from late 14c. Old English unlofod meant "unpraised."
He that can love unloved again,
Hath better store of love than brain
[Robert Ayton (1570-1638)]
unlovely (adj.): late 14c., "not evoking feelings of love," from un- (1) "not" + lovely. Meaning "ugly" is recorded from 1390s.
unlucky (adj.): 1520s, "marked by misfortune or failure," from un- (1) "not" + lucky (adj.). Similar formation in West Frisian unlokkich, Mliddle Low German unluckich. Sense of "boding ill" is recorded from 1540s; that of "having bad luck" is from 1550s; that of "bringing bad luck" is from 1580s. Related: Unluckily; unluckiness.
unmade (adj.): mid-13c., "not yet made, unfinished, incomplete," from un- (1) "not" + past participle of make (v.).
unmake (v.): late 14c., "bring down, dethrone;" early 15c., "undo, destroy, reduce to an unmade state," from un- (2) "reverse, opposite of" + make (v.). Similar formation in Middle Dutch ontmaken, German entmachen.
unmaking (n.): "ruin, destruction," 1590s, verbal noun from unmake (v.).
unman (v.): 1590s, "to deprive of the attributes of a human being," from un- (2) + verbal derivative of man (n.). Meaning "to deprive of manly courage" is attested from c. 1600; that of "to emasculate" is from 1680s.
unmanageable (adj.): 1630s, from un- (1) "not" + manageable (adj.). Related: Unmanageably; unmanageableness.
unmanaged (adj.): c. 1600, from un- (1) "not" + past participle of manage (v.).
unmanly (adj.): late 15c., "degrading to a human,"from un- (1) "not" + manly (adj.). Similar formation in Middle Dutch onmamlijc, German unmännlich. Meaning "not having the qualities or attributes of a man" (as opposed to a woman or child) is from 1540s. Old English had unmennisclic "inhuman" (adj.); unmann (n.) "monster; wicked man."
unmanned (adj.): "not furnished with a crew," 1540s, from un- (1) "not" + past participle of man (v).
unmannerly (adj.): late 14c., from un- (1) "not" + mannerly (adj.).
unmarked (adj.): c. 1400, "having been given no mark," from un- (1) "not" + past participle of mark (v.). Similar formation in Old Norse umarkaðr. Meaning "not noticed or observed" is recorded from 1530s.
unmarketable (adj.): 1650s, from un- (1) "not" + marketable (adj.).
unmarred (adj.): c. 1200, from un- (1) "not" + past participle of mar (v.).
unmarried (adj.): c. 1300, from un- (1) "not" + past participle of marry (v.). In former use most often applied to one who has never married.
unmask (v.): 1580s in figurative sense, c. 1600 in literal sense (transitive and intransitive), from un- (2) "reverse, opposite of" + mask (v.). Related: Unmasked; unmasking.
unmastered (adj.): 1560s, from un- (1) "not" + past participle of master (v.).
unmatched (adj.): 1580s, "unrivaled," from un- (1) "not" + past participle of match (v.).
unmeaning (adj.): "having no signification," 1709, from un- (1) "not" + present participle of mean (v.).
unmeasurable (adj.): late 14c., from un- (1) "not" + measurable (adj.). Related: Unmeasurably.
unmediated (adj.): 1640s, from un- (1) "not" + past participle of mediate (v.).
unmeet (adj.): Old English unmæte "immoderate, excessive," from un- (1) "not" + meet (adj.). Similar formation in Old High German unmazi. Meanings "unfitting" and "unsuited" (for some purpose) are from 1520s.
unmentionable (adj.): 1837, from un- (1) "not" + mentionable (adj.). Humorous use of unmentionables "trousers" is attested from 1806 (see inexpressible); from 1910 as "underwear," both on notion of "articles of dress not to be mentioned in polite circles."
unmerciful (adj.): late 15c., from un- (1) "not" + merciful (adj.). Related: Unmercifully.
unmerited (adj.): 1640s, from un- (1) "not" + past participle of merit (v.).
"An ingenuous mind feels in unmerited praise the bitterest reproof. If you reject it you are unhappy, if you accept it you are undone." [Walter Savage Landor, "Imaginary Conversations"]