unadulterated (adj.) Look up unadulterated at Dictionary.com
1719, from un- (1) "not" + past participle of adulterate (v.).
unadvertised (adj.) Look up unadvertised at Dictionary.com
mid-15c., "uninformed, unadvised," from un- (1) + advertised. Sense of "not announced or made known" is from 1864.
unaffected (adj.) Look up unaffected at Dictionary.com
1580s, "not influenced, untouched in mind or feeling," from un- (1) "not" + past participle of affect (v.). Meaning "not adopted or assumed, genuine" is recorded from 1590s; that of "not acted upon or altered (by something)" is first attested 1830. Related: Unaffectedly; unaffectedness.
unafraid (adj.) Look up unafraid at Dictionary.com
early 15c., from un- (1) "not" + afraid.
unaided (adj.) Look up unaided at Dictionary.com
1660s, from un- (1) "not" + past participle of aid (v.).
unalienable (adj.) Look up unalienable at Dictionary.com
1610s, from un- (1) "not" + alienable. Related: Unalienably.
unalloyed (adj.) Look up unalloyed at Dictionary.com
1670s (figurative); 1760s (literal), from un- (1) "not" + past participle of alloy (v.).
unalterable (adj.) Look up unalterable at Dictionary.com
1610s, from un- (1) "not" + alterable. Related: Unalterably.
He reach'd a middle height, and at the stars,
Which are the brain of heaven, he look'd, and sank.
Around the ancient track march'd, rank on rank,
The army of unalterable law.

[George Meredith, "Lucifer in Starlight"]
unaltered (adj.) Look up unaltered at Dictionary.com
1550s, from un- (1) "not" + past participle of alter (v.).
unambiguous (adj.) Look up unambiguous at Dictionary.com
1630s, from un- (1) "not" + ambiguous. Related: Unambiguously; unambiguousness.
unanimity (n.) Look up unanimity at Dictionary.com
mid-15c., from Old French unanimite (14c.), from Late Latin unanimitatem (nominative unanimitas) "unanimity, concord," from unanimus (see unanimous).
unanimous (adj.) Look up unanimous at Dictionary.com
1610s, from Latin unanimus "of one mind, in union," from unus "one" (see one) + animus "mind" (see animus). Related: Unanimously.
unannounced (adj.) Look up unannounced at Dictionary.com
1775, from un- (1) "not" + past participle of announce (v.).
unanswerable (adj.) Look up unanswerable at Dictionary.com
1610s, "admitting of no answer," from un- (1) "not" + answerable.
unanswered (adj.) Look up unanswered at Dictionary.com
late 14c., from un- (1) "not" + past participle of answer (v.).
unanticipated (adj.) Look up unanticipated at Dictionary.com
1741, from un- (1) "not" + past participle of anticipate (v.).
unapologetic (adj.) Look up unapologetic at Dictionary.com
1834, from un- (1) "not" + apologetic. Related: Unapologetically.
unappeasable (adj.) Look up unappeasable at Dictionary.com
1560s, from un- (1) "not" + appeasable. Related: Unappeasably.
Desolate winds that cry over the wandering sea;
Desolate winds that hover in the flaming West;
Desolate winds that beat the doors of Heaven, and beat
The doors of Hell and blow there many a whimpering ghost;
O heart the winds have shaken, the unappeasable host
Is comelier than candles at Mother Mary's feet.

[W.B. Yeats, "The Unappeasable Host," 1899]
unappreciated (adj.) Look up unappreciated at Dictionary.com
1809, from un- (1) "not" + past participle of appreciate (v.).
unappreciative (adj.) Look up unappreciative at Dictionary.com
1834, from un- (1) "not" + appreciative. Related: Unappreciatively; unappreciativeness.
unapprehended (adj.) Look up unapprehended at Dictionary.com
1590s, "not understood;" 1610s, "not taken or arrested," from un- (1) "not" + past participle of apprehend (v.).
unapproachable (adj.) Look up unapproachable at Dictionary.com
1580s, of places, from un- (1) "not" + approachable. Of persons, "distant, aloof," attested from 1848. Related: Unapproachably.
unapproved (adj.) Look up unapproved at Dictionary.com
early 15c., from un- (1) "not" + past participle of approve (v.).
unarmed (adj.) Look up unarmed at Dictionary.com
c.1300, "with armor removed," from un- (1) "not" + armed, or else past participle adjective from unarm "strip of armor" (c.1300), from un- (2) "opposite of" + arm (v.). Meaning "not fitted to attack, weaponless" is from late 14c.
unary (adj.) Look up unary at Dictionary.com
1923, from Latin unus "one" (see one) on model of binary, etc.
unashamed (adj.) Look up unashamed at Dictionary.com
c.1500, implied in unashamedness, from un- (1) "not" + ashamed. Related: Unashamedly.
unasked (adj.) Look up unasked at Dictionary.com
mid-13c., "uninvited," from un- (1) "not" + past participle of ask (v.). Old English had ungeaxod.
unaspiring (adj.) Look up unaspiring at Dictionary.com
1680s, from un- (1) "not" + present participle of aspire (v.).
unassailable (adj.) Look up unassailable at Dictionary.com
1590s, from un- (1) "not" + assailable (see assail (v.)). Related: Unassailably.
unassimilated (adj.) Look up unassimilated at Dictionary.com
1748, from un- (1) "not" + past participle of assimilate (v.).
unassisted (adj.) Look up unassisted at Dictionary.com
1610s, from un- (1) "not" + past participle of assist (v.). Related: Unassistedly.
unassuming (adj.) Look up unassuming at Dictionary.com
"unpretentious, modest," 1726, from un- (1) "not" + present participle of assume (v.). Related: Unassumingly.
unattached (adj.) Look up unattached at Dictionary.com
late 15c., "not arrested or seized," from un- (1) "not" + past participle of attach (v.). Meaning "not associated with any body or institution" is recorded from 1796; sense of "single, not engaged or married" is first attested 1874.
unattainable (adj.) Look up unattainable at Dictionary.com
1660s, from un- (1) "not" + attainable.
unattended (adj.) Look up unattended at Dictionary.com
c.1600, "alone, unaccompanied," from un- (1) "not" + past participle of attend (v.). Meaning "with no one in attendance" is from 1796.
unattested (adj.) Look up unattested at Dictionary.com
1660s, from un- (1) "not" + past participle of attest (v.).
unattractive (adj.) Look up unattractive at Dictionary.com
1729, from un- (1) "not" + attractive. Related: Unattractively; unattractiveness.
unauthorized (adj.) Look up unauthorized at Dictionary.com
1590s, from un- (1) "not" + past participle of authorize (v.).
unavailability (n.) Look up unavailability at Dictionary.com
1855, from un- (2) "opposite of" + availability, or else from unavailable + -ity.
unavailable (adj.) Look up unavailable at Dictionary.com
1540s, "ineffectual," from un- (1) "not" + available. Meaning "incapable of being used" is recorded from 1855. Unavailing has taken up the older sense of the word.
unavailing (adj.) Look up unavailing at Dictionary.com
"ineffectual, useless," 1660s, from un- (1) "not" + availing. Also see unavailable.
unavoidable (adj.) Look up unavoidable at Dictionary.com
mid-15c., from un- (1) "not" + avoidable. Related: Unavoidably.
unaware (adj.) Look up unaware at Dictionary.com
1590a; see unawares.
unawares (adv.) Look up unawares at Dictionary.com
1530s, "without being aware," from un- (1) "not" + aware + adverbial genitive -s. Meaning "without being noticed" is recorded from 1660s. Form unaware is recorded from 1590s.
unbalance (v.) Look up unbalance at Dictionary.com
1856, from un- (2) "reverse, opposite of" + balance (v.).
unbalanced (adj.) Look up unbalanced at Dictionary.com
1640s, from un- (1) "not" + past participle of balance (v.). Earliest use is in reference to the mind, judgment, etc. Of material things, it is recorded from 1732.
unbar (v.) Look up unbar at Dictionary.com
late 14c., from un- (2) "reverse, opposite of" + bar (v.). Related: Unbarred; unbarring.
unbearable (adj.) Look up unbearable at Dictionary.com
mid-15c., from un- (1) "not" + bearable. Related: Unbearably. Old English had unberendlic.
unbeatable (adj.) Look up unbeatable at Dictionary.com
1897, from un- (1) "not" + beatable.
unbeaten (adj.) Look up unbeaten at Dictionary.com
late 13c., "not beaten or struck," from un- (1) + beaten. In the sense of "undefeated" it is first recorded 1757. Old English had ungebeaten "unwrought, unstruck."