unchecked (adj.) Look up unchecked at Dictionary.com
late 15c., from un- (1) "not" + past participle of check (v.).
unchivalrous (adj.) Look up unchivalrous at Dictionary.com
1814, from un- (1) "not" + chivalrous. Related: Unchivalrously; unchivalric.
unchristian (adj.) Look up unchristian at Dictionary.com
1550s, "not professing Christianity" (of persons), from un- (1) "not" + Christian (adj.). Meaning "at variance with Christian principles" (of actions) is recorded from 1580s.
unchurched (adj.) Look up unchurched at Dictionary.com
1680s, from un- (1) "not" + churched "committed or belonging to a church" (see church (v.)). A verb, unchurch "to remove or exclude (someone) from membership in a church" is recorded from 1610s.
uncial (adj.) Look up uncial at Dictionary.com
1640s, "pertaining to an ounce," from Latin uncialis "of an inch, of an ounce," from uncia "a twelfth part" (see inch (n.1)). In reference to letters, it is attested from 1712, from Late Latin litterae unciales (Jerome), probably meaning "letters an inch high," from Latin uncialis "of an inch, inch-high." As a noun, "an uncial letter," from 1775.
uncirculated (adj.) Look up uncirculated at Dictionary.com
1749, from un- (1) "not" + past participle of circulate (v.).
uncircumcised (adj.) Look up uncircumcised at Dictionary.com
late 14c., from un- (1) "not" + past participle of circumcise (v.).
uncivil (adj.) Look up uncivil at Dictionary.com
1550s, "barbarous," from un- (1) "not" + civil (adj.). Meaning "impolite" is 1590s.
uncivilized (adj.) Look up uncivilized at Dictionary.com
c.1600, "barbarous," from un- (1) "not" + past participle of civilize (v.). Uncivil in the same sense is recorded from 1550s.
unclasp (v.) Look up unclasp at Dictionary.com
1520s, from un- (2) "reverse, opposite of" + clasp (v.). Related: Unclasped; unclasping.
unclassified (adj.) Look up unclassified at Dictionary.com
1813, from un- (1) "not" + past participle of classify.
uncle (n.) Look up uncle at Dictionary.com
late 13c., from Old French oncle, from Latin avunculus "mother's brother" ("father's brother" was patruus), literally "little grandfather," diminutive of avus "grandfather," from PIE root *awo- "grandfather, adult male relative other than one's father" (cognates: Armenian hav "grandfather," Lithuanian avynas "maternal uncle," Old Church Slavonic uji "uncle," Welsh ewythr "uncle").

Replaced Old English eam (usually maternal; paternal uncle was fædera), which represents the Germanic form of the root (cognates: Dutch oom, Old High German oheim "maternal uncle," German Ohm "uncle").

Also from French are German, Danish, Swedish onkel. As a familiar title of address to an old man, attested by 1793; in the U.S. South, especially "a kindly title for a worthy old negro" [Century Dictionary]. First record of Dutch uncle (and his blunt, stern, benevolent advice) is from 1838; Welsh uncle (1747) was the male first cousin of one's parent. To say uncle as a sign of submission in a fight is North American, attested from 1909, of uncertain signification.
Uncle Sam (n.) Look up Uncle Sam at Dictionary.com
symbol of the United States of America, 1813, coined during the war with Britain as a contrast to John Bull, and no doubt suggested by the initials U.S. in abbreviations. "[L]ater statements connecting it with different government officials of the name of Samuel appear to be unfounded" [OED]. The common figure of Uncle Sam began to appear in political cartoons c.1850. Only gradually superseded earlier Brother Jonathan (1776), largely through the popularization of the figure by cartoonist Thomas Nast. British in World War I sometimes called U.S. soldiers Sammies.
Uncle Tom (n.) Look up Uncle Tom at Dictionary.com
"servile black man," 1922, somewhat inaccurately in reference to the humble, pious, but strong-willed main character in Harriet Beecher Stowe's novel, "Uncle Tom's Cabin" (1852). The image implied in the insult perhaps is more traceable to the late 19c. minstel show versions of the story, which reached a far wider audience than the book.
I don't recall anyone in the 1920s using the term 'Uncle Tom' as an epithet. But what's amazing is how fast it caught on (in the 1930s). Black scholars picked up (the term) and just started throwing it at each other. [Ernest Allen, quoted in Hamilton, Kendra, "The Strange Career of Uncle Tom," Black Issues in Higher Education, June 2002]
As a verb, attested from 1937.
unclean (adj.) Look up unclean at Dictionary.com
Old English unclæne, "morally impure, defiled, unfit for food," from un- (1) "not" + clean (adj.). Literal sense of "dirty" is recorded from mid-13c.
uncleanly (adj.) Look up uncleanly at Dictionary.com
Old English unclænlic; see un- (1) "not" + cleanly (adj.). Related: Uncleanliness.
uncleanness (n.) Look up uncleanness at Dictionary.com
Old English unclænnes; see unclean + -ness.
unclear (adj.) Look up unclear at Dictionary.com
c.1300, "not easy to understand," from un- (1) "not" + clear (adj.). Similar formation in Middle Dutch onclaer, Dutch onklaar, German unklar, Old Norse uklarr, Danish uklar, Swedish oklar. Of persons, in sense of "uncertain, doubtful," it is recorded from 1670s.
uncleared (adj.) Look up uncleared at Dictionary.com
1630s in reference to debts, 1772 in reference to land; from un- (1) "not" + past participle of clear (v.).
unclog (v.) Look up unclog at Dictionary.com
c.1600, from un- (2) "reverse, opposite of" + clog (v.). Related: Unclogged; unclogging.
unclothe (v.) Look up unclothe at Dictionary.com
c.1300, uncloþe (transitive), from un- (2) "opposite of" + clothe (v.). Reflexive sense is attested from late 14c. Related: Unclothed; unclothing.
unclouded (adj.) Look up unclouded at Dictionary.com
1590s, from un- (1) "not" + past participle of cloud (v.).
uncoil (v.) Look up uncoil at Dictionary.com
1713 (transitive), from un- (2) "reverse, opposite of" + coil (v.). Related: Uncoiled; uncoiling.
uncollectable (adj.) Look up uncollectable at Dictionary.com
see uncollectible.
uncollected (adj.) Look up uncollected at Dictionary.com
1730, of things, from un- (1) "not" + past participle of collect (v.).
uncollectible (adj.) Look up uncollectible at Dictionary.com
1819, from un- (1) "not" + collectible. Form uncollectable is attested by 1796.
uncolored (adj.) Look up uncolored at Dictionary.com
also uncoloured, 1530s, from un- (1) "not" + past participle of color (v.). As a verb, from uncolor is recorded from early 15c.
uncomely (adj.) Look up uncomely at Dictionary.com
c.1200, "improper, unseemly, indecent," from un- (1) "not" + comely. Related: Uncomeliness.
uncomfortable (adj.) Look up uncomfortable at Dictionary.com
early 15c. "causing bodily or mental discomfort, affording no comfort," from un- (1) "not" + comfortable (adj.). Intransitive meaning "feeling discomfort, ill-at-ease" is attested from 1796. Related: Uncomfortably.
uncommitted (adj.) Look up uncommitted at Dictionary.com
late 14c., "not delegated," from un- (1) "not" + committed. Meaning "not pledged to any particular course or party" is attested from 1814.
uncommon (adj.) Look up uncommon at Dictionary.com
1540s, "not possessed in common," from un- (1) "not" + common (adj.). Meaning "not commonly occurring, unusual, rare" is recorded from 1610s. Related: Uncommonly.
uncommunicative (adj.) Look up uncommunicative at Dictionary.com
1690s, from un- (1) "not" + communicative.
uncomparable (adj.) Look up uncomparable at Dictionary.com
late 14c., "incomparable," from un- (1) "not" + comparable. Meaning "unable to be compared (to something else)" is from 1826. Related: Uncomparably.
uncompassionate (adj.) Look up uncompassionate at Dictionary.com
1590s, from un- (1) "not" + compassionate (adj.).
uncompensated (adj.) Look up uncompensated at Dictionary.com
1774, "not compensated by any good," from un- (1) "not" + past participle of compensate (v.). Meaning "not recompensed" is attested from 1830.
uncomplaining (adj.) Look up uncomplaining at Dictionary.com
1744, from un- (1) "not" + past participle of complain (v.).
uncomplicated (adj.) Look up uncomplicated at Dictionary.com
1724, from un- (1) "not" + complicated.
uncompounded (adj.) Look up uncompounded at Dictionary.com
1580s, from un- (1) "not" + past participle of compound (v.).
uncomprehending (adj.) Look up uncomprehending at Dictionary.com
1795, from un- (1) "not" + present participle of comprehend (v.). Related: Uncomprehendingly.
uncomprehensible (adj.) Look up uncomprehensible at Dictionary.com
late 14c., from un- (1) "not" + comprehensible. The usual word is incomprehensible.
uncompromised (adj.) Look up uncompromised at Dictionary.com
1775, from un- (1) "not" + past participle of compromise (v.).
uncompromising (adj.) Look up uncompromising at Dictionary.com
1799, from un- (1) "not" + present participle of compromise (v.). Related: Uncompromisingly.
unconcerned (adj.) Look up unconcerned at Dictionary.com
1630s, from un- (1) "not" + past participle of concern (v.). Related: Unconcernedly.
unconditional (adj.) Look up unconditional at Dictionary.com
1660s, from un- (1) "not" + conditional (adj.). Related: Unconditionally. Unconditional surrender in the military sense is attested from 1730; in U.S., often associated with Civil War Gen. Ulysses S. Grant and the taking of Fort Donelson.
The ringing phrase of Grant's latest despatch circulated through the North like some coinage fresh from the mint, and "Unconditional Surrender," which suited the initials of his modest signature, became like a baptismal name. [James Schouler, "History of the United States of America," Dodd, Mead & Co., 1899].
unconditioned (adj.) Look up unconditioned at Dictionary.com
1630s, from un- (1) "not" + past participle of condition (v.).
unconfined (adj.) Look up unconfined at Dictionary.com
c.1600, from un- (1) "not" + past participle of confine (v.).
unconfirmed (adj.) Look up unconfirmed at Dictionary.com
1560s, "not having received the rite of confirmation," from un- (1) "not" + confirmed. Meaning "not supported by further evidence" is attested from 1670s.
unconformable (adj.) Look up unconformable at Dictionary.com
1590s, from un- (1) "not" + past participle of conformable (v.).
unconformity (n.) Look up unconformity at Dictionary.com
c.1600, from un- (1) "not" + conformity. Geological sense is from 1829.
uncongenial (adj.) Look up uncongenial at Dictionary.com
1749, from un- (1) "not" + congenial (adj.).