unbecoming (adj.) Look up unbecoming at Dictionary.com
1590s, from un- (1) "not" + becoming "fitting." Related: Unbecomingly.
unbefitting (adj.) Look up unbefitting at Dictionary.com
1580s, from un- (1) "not" + befitting.
unbefriended (adj.) Look up unbefriended at Dictionary.com
from un- (1) "not" + past participle of befriend (v.).
unbegotten (adj.) Look up unbegotten at Dictionary.com
1530s, from un- (1) "not" + begotten.
unbegun (adj.) Look up unbegun at Dictionary.com
Old English unbegunnen; see un- (1) "not" + begun.
unbeknown (adj.) Look up unbeknown at Dictionary.com
"unknown," 1630s, from un- (1) "not" + beknown (see beknow).
unbeknownst (adj.) Look up unbeknownst at Dictionary.com
1833, vulgar formation from unbeknown (1630s). No clear reason for the -st, but since 19c. this has become the dominant form.
unbelief (n.) Look up unbelief at Dictionary.com
mid-12c., "absence or lack of religious belief; disbelief of the truth of the Gospel," from un- (1) "not" or un- (2) "opposite of" + belief. Old English had ungeleafa in this sense.
unbelievable (adj.) Look up unbelievable at Dictionary.com
1540s, from un- (1) "not" + believable. Related: Unbelievably.
unbeliever (n.) Look up unbeliever at Dictionary.com
"one who does not believe in any given religion," 1520s, from un- (1) "not" believer. Old English had ungelifend in this sense.
unbend (v.) Look up unbend at Dictionary.com
mid-13c., "relax a bow by unstringing it," from un- (2) "reverse, opposite of" + bend (v.). Intransitive sense from 1746. Figurative meaning "to become genial, relax" (1748) has a sense opposite to that of unbending "inflexible, obstinate" (1680s), which does not derive from the bow-stringing image.
unbeseeming (adj.) Look up unbeseeming at Dictionary.com
1580s, "not befitting, inappropriate, unsuitable," from un- (1) "not" + beseeming. A common 17c. word.
unbesought (adj.) Look up unbesought at Dictionary.com
1660s, from un- (1) "not" + besought.
unbias (v.) Look up unbias at Dictionary.com
"to free from bias," 1708, from un- (2) "reverse, opposite of" + bias (v.).
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.) Look up unbiased at Dictionary.com
c.1600, literal, in reference to throws at bowls, from un- (1) "not" + biased. Figurative sense of "impartial, unprejudiced" is recorded from 1640s.
unbidden (adj.) Look up unbidden at Dictionary.com
Old English unbedene, "not asked or invited," from un- (1) "not" + bidden. Similar formation in Middle Dutch ongebeden, German ungebeten, Old Norse ubeðinn.
unbind (v.) Look up unbind at Dictionary.com
Old English unbindan, "to free from binding," from un- (2) "opposite of, reverse" + bind (v.). Similar formation in Old Frisian unbinda, 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.
unbleached (adj.) Look up unbleached at Dictionary.com
1530s, from un- (1) "not" + past participle of bleach (v.).
unblemished (adj.) Look up unblemished at Dictionary.com
c.1300, from un- (1) "not" + past participle of blemish (v.). Originally in moral sense; material sense is attested from mid-15c.
unblown (adj.) Look up unblown at Dictionary.com
"not yet bloomed," 1580s, from un- (1) "not" + past participle of blow (v.2).
Life is the rose's hope while yet unblown;
The reading of an ever-changing tale;

[Keats, "Sleep and Poetry"]
unborn (adj.) Look up unborn at Dictionary.com
Old English unboren "not yet born; stillborn," from un- (1) "not" + born. Similar formation in Old Frisian unbern, Dutch ongeboren, Old High German ungiporan, German ungeboren.
unbosom (v.) Look up unbosom at Dictionary.com
"disclose in confidence" (secret opinions or feelings), 1580s, from un- (1) + bosom.
unbounded (adj.) Look up unbounded at Dictionary.com
1590s, "not limited in extent," from un- (1) "not" + past participle of bound (v.1). Sense of "generous, profuse, liberal" is recorded from 1704. Related: Unboundedness.
unbowed (adj.) Look up unbowed at Dictionary.com
late 14c., "not bent," also figuratively "not subdued," from un- (1) "not" + past participle of bow (v.).
unbreakable (adj.) Look up unbreakable at Dictionary.com
late 15c.; see un- (1) "not" + breakable.
unbridled (adj.) Look up unbridled at Dictionary.com
late 14c., originally in figurative sense of "unrestrained, ungoverned," from un- (1) "not" + bridled (see bridle (v.)). Similar formation in Middle Dutch ongebreidelt. Literal sense of "not fitted with a bridle" (of horses) is not recorded before 1550s. The verb unbridle (see un- (2)) is attested from c.1400 in the literal sense; mid-15c. in the figurative sense.
unbroken (adj.) Look up unbroken at Dictionary.com
c.1300, in reference to vows or compacts, from un- (1) "not" + broken. Attested from late 15c. in reference to material things; 1510s in reference to courage, spirit, etc.; 1530s in reference to horses; 1560s in reference to the flow of time. Old English had ungebrocen.
unbuckle (v.) Look up unbuckle at Dictionary.com
late 14c., from un- (2) "reverse of" + buckle (v.1). Related: Unbuckled; unbuckling.
unburden (v.) Look up unburden at Dictionary.com
1530s, "to unload" (transitive), from un- (2) "reverse of" + burden (v.). Similar formation in German entbürden. Reflexive sense is recorded from 1580s. Related: Unburdened; unburdening.
unburied (adj.) Look up unburied at Dictionary.com
Old English unbyrged "unburied," from un- (1) "not" + past participle of bury (v.).
unbutton (v.) Look up unbutton at Dictionary.com
early 14c., from un- (2) "opposite of" + button (v.). Related: Unbuttoned; unbuttoning.
uncalled (adj.) Look up uncalled at Dictionary.com
c.1400, "not summoned," from un- (1) "not" + past participle of call (v.). Similar formation in Swedish okallad, Danish ukaldet. With for and sense of "unnecessary, intrusive" it is first attested 1610.
uncanny (adj.) Look up uncanny at Dictionary.com
1590s, "mischievous;" 1773 in the sense of "associated with the supernatural," originally Scottish and northern English, from un- (1) "not" + canny.
uncap (v.) Look up uncap at Dictionary.com
1560s, from un- (2) "reverse, opposite of" + cap (v.). Related: Uncapped; uncapping.
uncaring (adj.) Look up uncaring at Dictionary.com
1786, from un- (1) "not" + caring.
unceasing (adj.) Look up unceasing at Dictionary.com
late 14c., from un- (1) "not" + present participle of cease (v.). Related: Unceasingly (mid-14c.).
uncensored (adj.) Look up uncensored at Dictionary.com
1890, from un- (1) "not" + past participle of censor (v.).
unceremonious (adj.) Look up unceremonious at Dictionary.com
1580s, from un- (1) "not" + ceremonious. Related: Unceremoniously.
uncertain (adj.) Look up uncertain at Dictionary.com
c.1300, "of indeterminate time or occurrence," from un- (1) "not" + certain (adj.). Meaning "not fully confident" is recorded from late 14c. (implied in uncertainty). Related: Uncertainly.
uncertainty (n.) Look up uncertainty at Dictionary.com
late 14c., from uncertain + -ty.
unchain (v.) Look up unchain at Dictionary.com
1580s, from un- (2) "opposite of" + chain (v.). Figurative sense of "to liberate" is recorded from 1793. Related: Unchained; unchaining.
unchallenged (adj.) Look up unchallenged at Dictionary.com
1630s, from un- (1) "not" + past participle of challenge (v.).
unchangeable (adj.) Look up unchangeable at Dictionary.com
mid-14c., from un- (1) + changeable.
unchanged (adj.) Look up unchanged at Dictionary.com
late 14c., from un- (1) "not" + past participle of change (v.).
unchanging (adj.) Look up unchanging at Dictionary.com
1590s, from un- (1) "not" + present participle of change (v.).
uncharacteristic (adj.) Look up uncharacteristic at Dictionary.com
1753, from un- (1) "not" + characteristic (adj.). Related: Uncharacteristically.
uncharitable (adj.) Look up uncharitable at Dictionary.com
mid-15c., from un- (1) "not" + charitable (v.). Related: Uncharitably (late 14c.).
uncharted (adj.) Look up uncharted at Dictionary.com
1804, from un- (1) "not" + past participle of chart (v.).
unchartered (adj.) Look up unchartered at Dictionary.com
1805, from un- (1) "not" + past participle of charter (v.).
unchaste (adj.) Look up unchaste at Dictionary.com
late 14c., from un- (1) "not" + chaste.