unconstitutional (adj.) Look up unconstitutional at Dictionary.com
1734, from un- (1) "not" + constitutional (adj.). Related: Unconstitutionally.
unconstrained (adj.) Look up unconstrained at Dictionary.com
1640s, from un- (1) "not" + past participle of constrain (v.). Related: Unconstrainedly.
uncontested (adj.) Look up uncontested at Dictionary.com
1670s, from un- (1) "not" + contested.
uncontrollable (adj.) Look up uncontrollable at Dictionary.com
1570s, "irrefutable," from un- (1) "not" + controllable. From 1590s as "not subject to authority;" meaning "that cannot be restrained" is from 1640s. Related: Uncontrollably.
uncontrolled (adj.) Look up uncontrolled at Dictionary.com
1510s, from un- (1) "not" + past participle of control (v.).
uncontroverted (adj.) Look up uncontroverted at Dictionary.com
"not liable to be called into question," 1640s, from un- (1) "not" + past participle of controvert (v.).
unconventional (adj.) Look up unconventional at Dictionary.com
1832, from un- (1) "not" + conventional (adj.). "A 19 cent. epithet for a certain type of affectation" [Weekley]. Related: Unconventionally.
unconventionality (n.) Look up unconventionality at Dictionary.com
1849, with reference to Shelley, from unconventional + -ity.
unconverted (adj.) Look up unconverted at Dictionary.com
1640s, from un- (1) "not" + past participle of convert (v.).
unconvinced (adj.) Look up unconvinced at Dictionary.com
1670s, from un- (1) "not" + past participle of convince (v.). Unconvincing is recorded from 1650s.
uncool (adj.) Look up uncool at Dictionary.com
1953, in hipster slang, from un- (1) "not" + slang sense of cool (adj.).
uncooperative (adj.) Look up uncooperative at Dictionary.com
also uncoöperative, 1847, from un- + cooperative (adj.). Related: Uncooperatively.
uncoordinated Look up uncoordinated at Dictionary.com
1801, from un- (1) "not" + past participle of coordinate (v.).
uncorrupted (adj.) Look up uncorrupted at Dictionary.com
c. 1400, of organic matter, "not putrefied," from un- (1) "not" + past participle of corrupt (v.). From 1560s of persons, "not influenced by bribes."
uncorruptible (adj.) Look up uncorruptible at Dictionary.com
late 14c., from un- (1) "not" + corruptible (adj.).
uncountable (adj.) Look up uncountable at Dictionary.com
late 14c., from un- (1) "not" + count (v.) + -able.
uncounted (adj.) Look up uncounted at Dictionary.com
c. 1500, from un- (1) "not" + past participle of count (v.).
uncouple (v.) Look up uncouple at Dictionary.com
c. 1300, from un- (2) "opposite of" + couple (v.). Similar formation in Middle Dutch ontcoppelen. Related: Uncoupled; uncoupling.
uncouth (adj.) Look up uncouth at Dictionary.com
Old English uncuð "unknown, strange, unusual; uncertain, unfamiliar; unfriendly, unkind, rough," from un- (1) "not" + cuð "known, well-known," past participle of cunnan "to know" (see can (v.1)), from PIE root *gno- "to know." Meaning "strange, crude, clumsy" is first recorded 1510s. The compound (and the thing it describes) widespread in IE languages, such as Latin ignorantem, Old Norse ukuðr, Gothic unkunþs, Sanskrit ajnatah, Armenian ancanaut', Greek agnotos, Old Irish ingnad "unknown."
uncover (v.) Look up uncover at Dictionary.com
early 14c., from un- (2) "reverse of" + cover (v.). Earliest use is figurative; literal sense is attested from late 14c. Related: Uncovered; uncovering.
uncredited (adj.) Look up uncredited at Dictionary.com
1580s, from un- (1) "not" + past participle of credit (v.).
uncritical (adj.) Look up uncritical at Dictionary.com
1650s, from un- (1) "not" + critical. Similar formation in Dutch onkritisch, German unkritisch, Danish unkritisk. Related: Uncritically.
unction (n.) Look up unction at Dictionary.com
"act of anointing as a religious rite," late 14c., from Latin unctionem (nominative unctio) "anointing," from unctus, past participle of ungere "to anoint" (see unguent).
unctious (adj.) Look up unctious at Dictionary.com
common variant of unctuous c. 1600-1725.
unctuous (adj.) Look up unctuous at Dictionary.com
late 14c., "oily, having a greasy or soapy feeling when touched," from Old French unctueus, from Medieval Latin unctuosus "greasy," from Latin unctus "act of anointing," from past participle stem of unguere "to anoint" (see unguent).

Figurative sense of "blandly ingratiating" is first recorded 1742, perhaps in part with a literal sense, but in part a sarcastic usage from unction in the meaning "deep spiritual feeling" (1690s), such as comes from having been anointed in the rite of unction. Related: Unctuously; unctuousness.
uncultivated (adj.) Look up uncultivated at Dictionary.com
1640s (figurative); 1680s (of plants); 1690s (of land), from un- (1) "not" + past participle of cultivate (v.).
uncurbed (adj.) Look up uncurbed at Dictionary.com
1590s, from un- (1) "not" + past participle of curb (v.).
uncurious (adj.) Look up uncurious at Dictionary.com
1560s, "not inquisitive," from un- (1) "not" + curious (adj.). From 1680s as "not odd or strange."
uncurl (v.) Look up uncurl at Dictionary.com
1580s, intransitive; 1590s, transitive," from un- (2) "reverse, opposite of" + curl (v.).
uncut (adj.) Look up uncut at Dictionary.com
early 15c., "not gashed or wounded," from un- (1) "not" + past participle of cut (v.). Of books, "not having the leaves slit open" it is recorded from 1828; of plays, etc., "without excisions," it is attested from 1896.
undated (adj.) Look up undated at Dictionary.com
"left without indication of date," 1560s, from un- (1) "not" + past participle of date (v.1) "assign a date to." Compare similarly formed German undatirt, Dutch ongedateerd, Swedish odaterad.
undaunted (adj.) Look up undaunted at Dictionary.com
mid-15c., with reference to horses, "untamed, not broken in," from un- (1) "not" + past participle of daunt (v.). In reference to persons, "intrepid," it is recorded from 1580s.
undaunting (adj.) Look up undaunting at Dictionary.com
1786, "not quailing" [OED], from un- (1) "not" + present participle of daunt (v.).
undead (adj.) Look up undead at Dictionary.com
"neither dead nor alive," c. 1400, from un- (1) "not" + dead. As a noun meaning "vampires and such," from 1904. Old English undeadlic (adv.) meant "immortal, for all eternity."
undeceive (v.) Look up undeceive at Dictionary.com
"to free from deception," 1590s, from un- (2) "opposite of" + deceive (v.).
undeceived (adj.) Look up undeceived at Dictionary.com
c. 1400, "reliable, accurate, certain," from un- (1) "not" + past participle of deceive (v.).
undecennial (adj.) Look up undecennial at Dictionary.com
"occurring every 11 years," 1858, in reference to solar activity cycle, from Latin undecim "eleven" + ending from biennial, etc.
undecided (adj.) Look up undecided at Dictionary.com
1530s, "not decided, unsettled," from un- (1) "not" + past participle of decide (v.).
undecipherable (adj.) Look up undecipherable at Dictionary.com
1758, from un- (1) "not" + decipherable (see decipher (v.)).
undecisive (adj.) Look up undecisive at Dictionary.com
1660s, from un- (1) "not" + decisive. The usual word is indecisive.
undefeated (adj.) Look up undefeated at Dictionary.com
1701, from un- (1) "not" + past participle of defeat (v.).
undefended (adj.) Look up undefended at Dictionary.com
1560s, "not defended, unprotected," from un- (1) "not" + past participle of defend (v.). Attested earlier in a now-obsolete sense of "unforbidden" (late 14c.).
undefiled (adj.) Look up undefiled at Dictionary.com
c. 1300, undefylde, from un- (1) "not" + past participle of defile (v.). Originally of morals; sexual sense is attested from mid-15c. Physical sense of "not made dirty" is from 1580s.
undefinable (adj.) Look up undefinable at Dictionary.com
"indefinable," 1650s, from un- (1) "not" + definable (see define). Related: Undefinably; undefinability.
undefined (adj.) Look up undefined at Dictionary.com
1610s, from un- (1) "not" + past participle of define (v.).
undelivered (adj.) Look up undelivered at Dictionary.com
late 15c., from un- (1) "not" + past participle of deliver (v.).
undemanding (adj.) Look up undemanding at Dictionary.com
1879, from un- (1) "not" + demanding (adj.).
undemonstrative (adj.) Look up undemonstrative at Dictionary.com
1826, "not characterized by outward expression of feelings," from un- (1) "not" + demonstrative (adj.).
undeniable (adj.) Look up undeniable at Dictionary.com
1540s, from un- (1) "not" + deny + -able. In 19c., often with a sense of "undeniably good." Related: Undeniably.
under (prep., adv.) Look up under at Dictionary.com
Old English under (prep.) "beneath, among, before, in the presence of, in subjection to, under the rule of, by means of," also, as an adverb, "beneath, below, underneath," expressing position with reference to that which is above, from Proto-Germanic *under- (source also of Old Frisian under, Dutch onder, Old High German untar, German unter, Old Norse undir, Gothic undar), from PIE *ndher- "under" (source also of Sanskrit adhah "below;" Avestan athara- "lower;" Latin infernus "lower," infra "below").

Productive as a prefix in Old English, as in German and Scandinavian (often forming words modeled on Latin ones in sub-). Notion of "inferior in rank, position, etc." was present in Old English. With reference to standards, "less than in age, price, value," etc., late 14c. As an adjective, "lower in position; lower in rank or degree" from 13c. Also used in Old English as a preposition meaning "between, among," as still in under these circumstances, etc. (though this may be an entirely separate root; see understand).

Under the weather "indisposed" is from 1810. Under the table is from 1921 in the sense of "very drunk," 1940s in sense of "illegal" (under-board "dishonest" is from c. 1600). To get something under (one's) belt is from 1954; to keep something under (one's) hat "secret" is from 1885; to have something under (one's) nose "in plain sight" is from 1540s; to speak under (one's) breath "in a low voice" is attested from 1832. To be under (someone's) thumb "entirely controlled" (by that person) is recorded from 1754.