undine (n.) Look up undine at Dictionary.com
female water spirit, 1821, from Modern Latin Undina (1650s), coined by Paracelsus ("De Nymphis") in his alchemical system, from Latin unda "a wave, billow" (see water (n.1)). Popularized by German romance "Undine, eine Erzählung" (1811) by Baron F.H.C. La Motte Fouqué. Undinism (1928) was coined by sex researcher Havelock Ellis to describe the fetish for urine (which Ellis had); nowadays it would be called urophilia.
undisciplined (adj.) Look up undisciplined at Dictionary.com
late 14c., "untrained," from un- (1) "not" + past participle of discipline (v.). Similar formation in German undisciplinirt, Swedish odisciplinerad. Specific meaning "not subject to military discipline" is attested from 1718.
undisclosed (adj.) Look up undisclosed at Dictionary.com
1560s, from un- (1) "not" + past participle of disclose (v.).
undiscovered (adj.) Look up undiscovered at Dictionary.com
1540s, from un- (1) "not" + past participle of discover (v.).
undisguised (adj.) Look up undisguised at Dictionary.com
c.1500, in reference to things, from un- (1) "not" + past participle of disguise (v.). Of persons, attested from 1670s.
undismayed (adj.) Look up undismayed at Dictionary.com
1610s, from un- (1) "not" + past participle of dismay (v.).
undisputable (adj.) Look up undisputable at Dictionary.com
1590s, from un- (1) "not" + disputable (see dispute (v.)). The usual word is indisputable. Related: Undisputably.
undisputed (adj.) Look up undisputed at Dictionary.com
1560s, "not argued with," from un- (1) "not" + past participle of dispute (v.). Meaning "not called into question" is attested from 1620s.
undistinguishable Look up undistinguishable at Dictionary.com
1580s, from un- (1) “not” + distinguishable.
undistinguished (adj.) Look up undistinguished at Dictionary.com
1590s, "not kept distinct," from un- (1) "not" + distinguished. Meaning "not elevated above others" is attested from c.1600.
undisturbed (adj.) Look up undisturbed at Dictionary.com
c.1600, from un- (1) "not" + past participle of disturb (v.).
undivided (adj.) Look up undivided at Dictionary.com
early 15c., from un- (1) "not" + past participle of divide (v.).
undivulged (adj.) Look up undivulged at Dictionary.com
c.1600, from un- (1) "not" + past participle of divulge (v.).
undo (v.) Look up undo at Dictionary.com
Old English undon "to unfasten and open" (a window or door), "to unfasten by releasing from a fixed position; to cancel, discharge, abrogate, reverse what has been done, put back in a former condition; bring to ruin, destroy," from un- (2) "opposite of" + do (v.). Related: Undone; undoing.
undocumented (adj.) Look up undocumented at Dictionary.com
1883, from un- (1) "not" + past participle of document (v.).
undomesticated (adj.) Look up undomesticated at Dictionary.com
1834, from un- (1) "not" + past participle of domesticate (v.). Undomestic "not caring for home life" is recorded from 1754.
undone (adj.) Look up undone at Dictionary.com
"not accomplished," c.1300, from un- (1) "not" + done. The same word meaning "destroyed" is recorded from mid-14c., past participle adjective from undo.
undoubtable (adj.) Look up undoubtable at Dictionary.com
early 15c., from un- (1) "not" + doubt (v.) + -able. Related: Undoubtably.
undoubted (adj.) Look up undoubted at Dictionary.com
mid-15c., from un- (1) "not" + past participle of doubt (v.). Related: Undoubtedly.
undreamed (adj.) Look up undreamed at Dictionary.com
1610s, from un- (1) "not" + past participle of dream (v.).
undress (v.) Look up undress at Dictionary.com
1590s, "to shed one's clothing," from un- (2) "opposite of" + dress (v.). Transitive sense of "to strip off (someone's) clothing" is recorded from 1610s. Related: Undressed; undressing.
undress (n.) Look up undress at Dictionary.com
"state of partial or incomplete dress," 1680s, from undress (v.). Meaning "ordinary dress" is from 1748.
undressed (adj.) Look up undressed at Dictionary.com
"naked (or nearly so)," 1610s, past participle adjective from undress (v.).
undue (adj.) Look up undue at Dictionary.com
late 14c., "not owing or payable; unjustly demanded," also "not appropriate, unseasonable," also "excessive," from un- (1) "not" + past participle of due (v.). Formed on model of Old French indeu, Latin indebitus.
undulant (adj.) Look up undulant at Dictionary.com
1830, from Latin undulantem (nominative undulans), from unda "wave" (see water (n.1)).
undulate (v.) Look up undulate at Dictionary.com
"to move in waves," 1660s, back-formation from undulation. Related: undulated, undulating.
undulation (n.) Look up undulation at Dictionary.com
1640s, from Medieval Latin *undulatio, from Late Latin undulatus "wavy, undulated," from undula "wavelet," diminutive of Latin unda "wave" (see water (n.1)).
unduly (adv.) Look up unduly at Dictionary.com
late 14c., "without due moderation; improperly, unsuitably;" see undue + -ly (2). From early 15c. as "unjustly, wrongfully."
undying (adj.) Look up undying at Dictionary.com
c.1300, "immortal," from un- (1) "not" + present participle of die (v.). Figurative sense, of feelings, etc., is recorded from c.1765.
une (v.) Look up une at Dictionary.com
"to unite," c.1400, from Latin unire, from unus "one" (see one).
unearned (adj.) Look up unearned at Dictionary.com
c.1200, from un- (1) "not" + past participle of earn (v.). Unearned income is recorded from 1889.
unearth (v.) Look up unearth at Dictionary.com
"to dig up," mid-15c., from un- (2) "opposite of" + earth (v.) "bury (a corpse) in the ground" (c.1400, from earth (n.)). Related: Unearthed; unearthing.
unearthly (adj.) Look up unearthly at Dictionary.com
1610s, "heavenly, sublime," from un- (1) "not" + earthly. Sense of "ghostly, weird" first recorded 1802. Related: Unearthliness.
uneasy (adj.) Look up uneasy at Dictionary.com
late 13c., "not comforting, causing trouble," from un- (1) "not" + easy (adj.). Meaning "disturbed in mind" is attested from 1670s. Related: Uneasily; uneasiness.
uneducated (adj.) Look up uneducated at Dictionary.com
1580s, from un- (1) "not" + past participle of educate (v.).
unelectable (adj.) Look up unelectable at Dictionary.com
also un-electable, 1962, from un- (1) "not" + electable.
unemancipated (adj.) Look up unemancipated at Dictionary.com
1775, from un- (1) "not" + past participle of emancipate (v.).
unemotional (adj.) Look up unemotional at Dictionary.com
1819, from un- (1) "not" + emotional (adj.). Related: Unemotionally.
unemployed (adj.) Look up unemployed at Dictionary.com
1600, "at leisure, not occupied," from un- (1) "not" + past participle of employ (v.). Meaning "temporarily out of work" is from 1660s. The noun meaning "unemployed persons collectively" is from 1782.
No man has hired us
With pocketed hands
And lowered faces
We stand about in open places
And shiver in unlit rooms ...

[T.S. Eliot, "Choruses from the Rock"]
unemployment (n.) Look up unemployment at Dictionary.com
1887, from un- (1) "not" + employment.
unencumbered (adj.) Look up unencumbered at Dictionary.com
1722, from un- (1) "not" + past participle of encumber (v.).
unending (adj.) Look up unending at Dictionary.com
1660s, from un- (1) "not" + present participle of end (v.).
unendurable (adj.) Look up unendurable at Dictionary.com
1620s, from un- (1) "not" + endurable. Related: Unendurably.
unenlightened (adj.) Look up unenlightened at Dictionary.com
1660s, "not lit up," from un- (1) "not" + past participle of enlighten (v.). Meaning "not mentally illuminated" is attested from 1650s.
unenthusiastic (adj.) Look up unenthusiastic at Dictionary.com
1805, from un- (1) "not" + enthusiastic (adj.). Related: Unenthusiastically.
unenviable (adj.) Look up unenviable at Dictionary.com
1640s, from un- (1) "not" + enviable (adj.). Related: Unenviably.
unequal (adj.) Look up unequal at Dictionary.com
1530s, "unjust, unfair," from un- (1) "not" + equal (adj.). Meaning "not the same in amount, size, quality, etc." is recorded from 1560s (inequal in this sense is from late 14c.). Sense of "inadequate, insufficient" (to some task) is attested from 1690s. Related: Unequally.
unequivocal (adj.) Look up unequivocal at Dictionary.com
1784, from un- (1) "not" + equivocal. Related: Unequivocally.
unerring (adj.) Look up unerring at Dictionary.com
1640s (implied in unerringly), from un- (1) "not" + verbal noun from err. Related: Unerringly.
UNESCO Look up UNESCO at Dictionary.com
acronym from United Nations Educational, Scientific and Cultural Organization, which was created in 1945.