Online Etymology Dictionary

undiscovered (adj.): 1540s, from un- (1) "not" + past participle of discover (v.).
undisguised (adj.): c. 1500, in reference to things, from un- (1) "not" + past participle of disguise (v.). Of persons, attested from 1670s.
undismayed (adj.): 1610s, from un- (1) "not" + past participle of dismay (v.).
undisputable (adj.): 1590s, from un- (1) "not" + disputable (see dispute (v.)). The usual word is indisputable. Related: Undisputably.
undisputed (adj.): 1560s, "not argued with," from un- (1) "not" + past participle of dispute (v.). Meaning "not called into question" is attested from 1620s.
undistinguishable: 1580s, from un- (1) "not" + distinguishable.
undistinguished (adj.): 1590s, "not kept distinct," from un- (1) "not" + distinguished. Meaning "not elevated above others" is attested from c. 1600.
undisturbed (adj.): c. 1600, from un- (1) "not" + past participle of disturb (v.).
undivided (adj.): early 15c., from un- (1) "not" + past participle of divide (v.).
undivulged (adj.): c. 1600, from un- (1) "not" + past participle of divulge (v.).
undo (v.): 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.): 1883, from un- (1) "not" + past participle of document (v.).
undomesticated (adj.): 1834, from un- (1) "not" + past participle of domesticate (v.). Undomestic "not caring for home life" is recorded from 1754.
undone (adj.): "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.): early 15c., from un- (1) "not" + doubt (v.) + -able. Related: Undoubtably.
undoubted (adj.): mid-15c., from un- (1) "not" + past participle of doubt (v.). Related: Undoubtedly.
undreamed (adj.): 1610s, from un- (1) "not" + past participle of dream (v.).
undress (v.): 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.): "state of partial or incomplete dress," 1680s, from undress (v.). Meaning "ordinary dress" is from 1748.
undressed (adj.): "naked (or nearly so)," 1610s, past participle adjective from undress (v.).
undue (adj.): 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.): 1830, from Latin undulantem (nominative undulans), from unda "a wave," from PIE *unda-, nasalized form of root *wed- (1) "water, wet" (see water (n.1)).
undulate (v.): "to move in waves," 1660s, back-formation from undulation. Related: undulated, undulating.
undulation (n.): 1640s, from Medieval Latin *undulatio, from Late Latin undulatus "wavy, undulated," from undula "wavelet," diminutive of Latin unda "a wave," from PIE *unda-, nasalized form of root *wed- (1) "water, wet" (see water (n.1)).
unduly (adv.): late 14c., "without due moderation; improperly, unsuitably;" see undue + -ly (2). From early 15c. as "unjustly, wrongfully."
undying (adj.): c. 1300, "immortal," from un- (1) "not" + present participle of die (v.). Figurative sense, of feelings, etc., is recorded from c. 1765.
une (v.): "to unite," c. 1400, from Late Latin unire "to make into one" (transitive), from unus "one" (see one).
unearned (adj.): c. 1200, from un- (1) "not" + past participle of earn (v.). Unearned income is recorded from 1889.
unearth (v.): "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.): 1610s, "heavenly, sublime," from un- (1) "not" + earthly. Sense of "ghostly, weird" first recorded 1802. Related: Unearthliness.
uneasy (adj.): 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.): 1580s, from un- (1) "not" + past participle of educate (v.).
unelectable (adj.): also un-electable, 1962, from un- (1) "not" + electable.
unemancipated (adj.): 1775, from un- (1) "not" + past participle of emancipate (v.).
unemotional (adj.): 1819, from un- (1) "not" + emotional (adj.). Related: Unemotionally.
unemployed (adj.): 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.): 1887, from un- (1) "not" + employment.
unencumbered (adj.): 1722, from un- (1) "not" + past participle of encumber (v.).
unending (adj.): 1660s, from un- (1) "not" + present participle of end (v.).
unendurable (adj.): 1620s, from un- (1) "not" + endurable. Related: Unendurably.
unenlightened (adj.): 1660s, "not lit up," from un- (1) "not" + past participle of enlighten (v.). Meaning "not mentally illuminated" is attested from 1650s.
unenthusiastic (adj.): 1805, from un- (1) "not" + enthusiastic (adj.). Related: Unenthusiastically.
unenviable (adj.): 1640s, from un- (1) "not" + enviable (adj.). Related: Unenviably.
unequal (adj.): 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.): 1784, from un- (1) "not" + equivocal. Related: Unequivocally.
unerring (adj.): 1640s (implied in unerringly), from un- (1) "not" + verbal noun from err. Related: Unerringly.
UNESCO: acronym from United Nations Educational, Scientific and Cultural Organization, which was created in 1945.
unethical (adj.): 1871, from un- (1) "not" + ethical. Related: Unethically.
uneven (adj.): Old English unefen "unequal, unlike, anomalous, irregular," from un- (1) "not" + even (adj.). Similar formation in Old Frisian oniovn, Middle Dutch oneven, Old High German uneban, German uneben, Old Norse ujafn. Meaning "broken, rugged" (in reference to terrain, etc.) is recorded from late 13c. Related: Unevenly; unevenness.
uneventful (adj.): 1800, from un- (1) "not" + eventful. Related: Uneventfully.