Online Etymology Dictionary

uninteresting (adj.): 1769, from un- (1) "not" + interesting.
uninterrupted (adj.): c.1600, from un- (1) "not" + past participle of interrupt. Related: Uninterruptedly.
uninvited: 1630s, from un- (1) "not" + past participle of invite (v.). Related: Uninvited; uninviting, which was used as a past participle adjective from 1680s.
union (n.): early 15c., "action of joining one thing to another," from Old French union (12c.), from Late Latin unionem (nominative unio) "oneness, unity, a uniting," also in Latin meaning "a single pearl or onion," from unus "one," from PIE *oinos (see one).

Sense of "action of uniting into one political body" is attested from 1540s. Meaning "group of people or states" is from 1650s. Short for trade union, it is recorded from 1833. U.S. political sense is attested from 1775; used especially during the Civil War, in reference to the remainder of the United States after the Southern secession.
Union Jack: 1670s, from union + jack (n.); properly a small British union flag flown as the jack of a ship, but it has long been in use as a general name for the union flag. The Union flag (1630s) was introduced to symbolize the union of the crowns of England and Scotland (in 1603) and was formed of a combination of the cross saltire of St. Andrew and the cross of St. George. The cross saltire of St. Patrick was added 1801 upon the union of parliaments of Great Britain and Ireland.
unionize (v.): "make into a union," 1841, from union + -ize. Related: Unionized; unionizing.
unipolar (adj.): 1812, from uni- + polar.
unique (adj.): c.1600, "single, solitary," from French unique, from Latin unicus "single, sole," from unus "one" (see one). Meaning "forming the only one of its kind" is attested from 1610s; erroneous sense of "remarkable, uncommon" is attested from mid-19c.
unisex (adj.): "sexually indistinguishable or neutral," 1968, from uni- + sex (n.).
unison (n.): 1570s, from Middle French unisson "unison, accord of sound" (16c.), from Medieval Latin unisonus "having one sound, sounding the same," from Late Latin unisonius "in immediate sequence in the scale, monotonous," from Latin uni- "one" (see one) + sonus "sound" (see sound (n.1)). Sense of "harmonious agreement" is first attested 1640s.
unit (n.): 1560s, "single number regarded as an undivided whole," alteration of unity on the basis of digit. Popularized in John Dee's English translation of Euclid, to express Greek monas (Dee says unity formerly was used in this sense). Meaning "single thing regarded as a member of a group" is attested from 1640s. Extended sense of "a quantity adopted as a standard of measure" is from 1738. Sense of "group of wards in a hospital" is attested from 1893.
unitarian (n.): 1680s, "one who rejects the doctrine of the Trinity," from Modern Latin unitarius (1650s), from Latin unitas (see unity) + -ian.
unitary (adj.): 1816; see unit + -ary.
unite (v.): early 15c., from Latin unitus, past participle of unire "to unite," from unus "one" (see one). Related: United; uniting.
United Kingdom: attested from 1737.
United Nations: 1942, "the Allied nations at war with the Axis powers;" the international body (officially the United Nations Organization) was chartered in 1945.
Such negotiation as may occur in New York is not conducted within the walls of the tall building by the East River: it is carried out elsewhere, in accordance with those principles of courtesy, confidence and discretion which must for ever remain the only principles conducive to the peaceful settlement of disputes. [Harold Nicholson, "The Evolution of Diplomatic Method," 1954]
united states (n.): attested from 1617, originally with reference to Holland; the North American confederation first so called in 1776. United Provinces were the seven northern provinces of the Netherlands, allied from 1579, later developing into the kingdom of Holland.
unity (n.): c.1300, from Anglo-French unite, Old French unite (c.1200), from Latin unitatem (nominative unitas) "oneness, sameness, agreement," from unus "one" (see one).
univalve: 1660s (noun and adjective), from uni- + valve.
universal (adj.): late 14c., from Old French universel (12c.), from Latin universalis "of or belonging to all," from universus "all together, whole, entire" (see universe). In mechanics, a universal joint (1670s) is one which allows free movement in any direction; in theology universalism (1805) is the doctrine of universal salvation (universalist in this sense is attested from 1620s). Universal product code is recorded from 1974.
universalism (n.): 1805, from universal + -ism.
universality (n.): late 14c., from Old French universaliteit (14c.) or directly from Late Latin universalitas, from Latin universalis (see universal).
universally (adv.): late 14c., from universal + -ly (2).
universe (n.): 1580s, "the whole world, cosmos," from Old French univers (12c.), from Latin universum "the universe," noun use of neuter of adj. universus "all together," literally "turned into one," from unus "one" (see one) + versus, past participle of vertere "to turn" (see versus). Properly a loan-translation of Greek to holon "the universe," noun use of neuter of adj. holos "whole" (see safe (adj.)).
university (n.): c.1300, "institution of higher learning," also "body of persons constituting a university," from Anglo-French université, Old French universitei (13c.), from Medieval Latin universitatem (nominative universitas), in Late Latin "corporation, society," from Latin, "the whole, aggregate," from universus "whole, entire" (see universe). In the academic sense, a shortening of universitas magistrorum et scholarium "community of masters and scholars;" superseded studium as the word for this.
univocal (adj.): 1540s, from Latin univocus, from uni- (see uni-) + vox (see voice (n.)).
unjust (adj.): late 14c., of persons, from un- (1) "not" + just (adj.). Of actions, attested from c.1400.
unjustifiable (adj.): 1640s, from un- (1) "not" + justifiable. Related: Unjustifiably.
unjustified (adj.): mid-14c., "not punished or executed," from un- (1) "not" + past participle of justify. Meaning "not proven to be right or proper" is attested from 1680s.
unkempt (adj.): 1570s, from un- (1) "not" + kempt "well-combed, neat," from variant past participle of Old English cemban "to comb," from Proto-Germanic *kambijan, from *kamb- "comb" (see comb). Form unkembed is recorded from late 14c. The verb kemb is rare after 1400s, but its negative past participle form endures.
unkept (adj.): mid-14c., from un- (1) "not" + past participle of keep (v.).
unkind (adj.): early 13c. (implied in unkindly), "strange, foreign, unnatural," from un- (1) "not" + kind (adj.). Meaning "lacking in kindness" is recorded from mid-14c. Related: Unkindly; unkindness.
unknowing (adj.): c.1300, "without knowledge, ignorant," from un- (1) "not" + present participle of know (v.). Noun meaning "ignorance" is mid-14c. Related: Unknowingly.
unknown (adj.): c.1300, "strange, unfamiliar" (of persons, places), from un- (1) "not" + past participle of know. Cf. Old English ungecnawen. In reference to facts, attested from early 14c. The noun meaning "unknown person" is recorded from 1590s.
unlace (v.): c.1300, from un- (2) + lace (v.). Related: Unlaced; unlacing.
unladen (adj.): 1802, from unlade, Old English onhladen; see un- (1) "not" + laden.
unlamented (adj.): 1590s, from un- (1) "not" + past participle of lament (v.).
unlawful (adj.): c.1300, from un- (1) "not" + lawful. Unlawful assembly is recorded in statutes from late 15c. Related: Unlawfully.
unleaded (adj.): 1610s, from un- (1) "not" + leaded (see lead (n.)). In reference to gasoline, from 1965.
unleash (v.): 1670s, from un- (2) + leash (v.). Related: Unleashed; unleashing.
unleavened (adj.): 1520s, from un- (1) "not" + past participle of leaven.
unless: mid-15c., earlier onlesse, from on lesse (than) "on a less condition (than)," the first syllable originally on, but the negative connotation and the lack of stress changed it to un-.
unlettered (adj.): mid-14c., "not possessed of book-learning," from un- (1) "not" + lettered (see letter (n.)). An anglicized form of illiterate. Cf. Middle Dutch ongelettert.
unlicensed (adj.): 1630s, from un- (1) "not" + past participle of licence (v.).
unlike: c.1200, "not resembling," from un- (1) "not" + like. Cf. Old English ungelic, Old Frisian unlik, Old Norse ulikr, M.Da. ulige.
unlikely: late 14c., "not likely to occur," from un- (1) + likely. Cf. Old Norse ulikligr, M.Da. uligelig. Meaning "not likely to be true" is recorded from 1590s.
unlimber (v.): 1802, "to free (a gun) from its limber," usually for the purpose of bringing it into action, from un- (2) + limber (n.). Figurative sense is attested from 1864. Related: Unlimbered; unlimbering.
unlimited (adj.): mid-15c., from un- (1) "not" + past participle of limit (v.).
unlisted (adj.): 1640s, from un- (1) "not" + past participle of list (v.). In reference to stocks, attested from 1905; of phone numbers, from 1937 (American English).
unlivable (adj.): 1869, from un- (1) "not" + livable.