Online Etymology Dictionary

unanimity (n.): mid-15c., from Old French unanimite (14c.), from Latin unanimitas, from unanimus (see unanimous).
unanimous (adj.): 1610s, from Latin unanimus "of one mind," from unus "one" (see one) + animus "mind" (see animus). Related: Unanimously.
unannounced (adj.): 1775, from un- (1) "not" + past participle of announce.
unanswered (adj.): late 14c., from un- (1) "not" + past participle of answer.
unanticipated (adj.): 1741, from un- (1) "not" + past participle of anticipate.
unapologetic (adj.): 1834, from un- (1) "not" + apologetic. Related: Unapologetically.
unappeasable (adj.): 1560s, from un- (1) "not" + appeasable. Related: Unappeasably.
unappreciated (adj.): 1809, from un- (1) "not" + past participle of appreciate.
unappreciative (adj.): 1834, from un- (1) "not" + appreciative. Related: Unappreciatively; unappreciativeness.
unapproachable (adj.): 1580s, of places, from un- (1) "not" + approachable. Of persons, "distant, aloof," attested from 1848. Related: Unapproachably.
unapproved (adj.): early 15c., from un- (1) "not" + past participle of approve.
unarmed (adj.): c.1300, "with armor removed," from un- (1) "not" + armed.
unary (adj.): 1923, from Latin unus "one" (see one) on model of binary, etc.
unashamed (adj.): c.1500, implied in unashamedness, from un- (1) + ashamed. Related: Unashamedly.
unasked (adj.): mid-13c., "uninvited," from un- (1) "not" + past participle of ask.
unassailable (adj.): 1590s, from un- (1) "not" + assailable (see assail). Related: Unassailably.
unassisted (adj.): 1610s, from un- (1) "not" + past participle of assist (v.).
unassuming (adj.): "unpretentious," 1726, from un- (1) "not" + infinitive of assume.
unattached (adj.): late 15c., "not arrested or seized," from un- (1) "not" + past participle of attach. 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.): 1660s, from un- (1) "not" + attainable.
unattended (adj.): c.1600, "alone, unaccompanied," from un- (1) "not" + past participle of attend. Meaning "with no one in attendance" is from 1796.
unattractive (adj.): 1729, from un- (1) "not" + attractive. Related: Unattractively; unattractiveness.
unauthorized (adj.): 1590s, from un- (1) "not" + past participle of authorize.
unavailability (n.): 1855, from un- (1) "not" + availability.
unavailable (adj.): 1540s, "ineffectual," from un- (1) "not" + available. Meaning "incapable of being used" is recorded from 1855. Unavailing (1660s) has taken up the older sense of the word.
unavailing (adj.): 1660s, from un- (1) "not" + availing. Also see unavailable.
unavoidable (adj.): mid-15c., from un- (1) "not" + avoidable. Related: Unavoidably.
unaware: see unawares.
unawares (adv.): 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.
unbalanced (adj.): 1640s, from un- (1) "not" + past participle of balance. Earliest use is in reference to the mind, judgment, etc. Of material things, it is recorded from 1732.
unbearable (adj.): mid-15c., from un- (1) "not" + bearable. Related: Unbearably.
unbeatable (adj.): 1897, from un- (1) "not" + beatable.
unbeaten (adj.): late 13c., "not beaten or struck," from un- (1) + beaten. In the sense of "undefeated" it is first recorded 1757.
unbecoming (adj.): 1590s, from un- (1) "not" + becoming "fitting."
unbeknown (adj.): 1630s, from un- (1) "not" + beknown (see beknow).
unbeknownst: 1833, vulgar formation from unbeknown (1630s). No clear reason for the -st, but since 19c. this has become the dominant form.
unbelief (n.): mid-12c., "absence or lack of religious belief," from un- (1) "not" + belief.
unbelievable (adj.): 1540s, from un- (1) "not" + believable. Related: Unbelievably.
unbeliever (n.): 1520s, agent noun from unbelief.
unbend (v.): "to relax a bow by unstringing it," mid-13c., from un- (2) + bend (v.). Figurative meaning "to become genial, relax" (1748) has a sense opposite to that of unbending "inflexible, obstinate" (1680s), which does not derive from the bowstringing image.
unbeseeming: 1580s, "not befitting, inappropriate," from un- (1) "not" + beseeming. A common 17c. word.
unbias (v.): "to free from bias," 1708, from un- (1) "not" + bias.
The truest service a private man may hope to do his country is, by unbiassing his mind as much as possible. [Swift, "The Sentiments of a Church of England Man with respect to Religion and Government," 1708]
unbiased (adj.): c.1600, literal, in reference to throws at bowls, from un- (1) "not" + biased. Figurative sense of "impartial, unprejudiced" is recorded from 1640s.
unbidden: Old English unbedene, "not asked or invited," from un- (1) "not" + bidden. Cf. Middle Dutch ongebeden, German ungebeten, Old Norse ubeðinn.
unbind (v.): Old English unbindan, "to free from binding," from un- (2) + bind (v.). Cf. German entbinden, Dutch ontbinden. Literal and figurative senses both present in Old English.
Suæ huæt ðu unbindes ofer eorðu bið unbunden in heofnum. [Lindisfarne Gospels, Matt. xvi:19]
Unbound is from Old English unbunden, in literal sense. Figurative sense first attested late 14c.; of books from 1540s.
unblemished (adj.): c.1300, from un- (1) "not" + past participle of blemish. Originally in moral sense; material sense is attested from mid-15c.
unborn (adj.): Old English unboren "not yet born; stillborn," from un- (1) "not" + born. Cf. Old Frisian unbern, Dutch ongeboren, Old High German ungiporan, German ungeboren.
unbounded (adj.): 1590s, "not limited in extent," from un- (1) "not" + past participle of bound (v.1). Sense of "generous, profuse, liberal" is recorded from 1704.
unbreakable (adj.): late 15c.; see un- (1) "not" + breakable.
unbridled (adj.): late 14c., originally in figurative sense of "unrestrained, ungoverned," from un- (1) "not" + bridled (see bridle (v.)). Cf. Middle Dutch ongebreidelt. Literal sense of "not fitted with a bridle" (of horses) is not recorded before 1550s. The verb unbridle is attested from c.1400 in the literal sense; mid-15c. in the figurative sense.