Online Etymology Dictionary

U: for historical evolution, see V. Used punningly for you by 1588 ["Love's Labour's Lost," V.i.60], not long after the pronunciation shift that made the vowel a homonym of the pronoun. As a simple shorthand (without intentional word-play), it is recorded from 1862. Common in business abbreviations since 1923 (such as U-Haul, attested from 1951).
U-bahn (n.): German or Austrian subway system, 1938 (originally in reference to Berlin), from German U-bahn, short for Untergrund-bahn, literally "underground railway."
U-boat (n.): 1916 (said to have been in use from 1913), partial translation of German U-Boot, short for Unterseeboot, literally "undersea boat."
U-turn (n.): 1934, from U + turn (n.). So called in reference to the shape of the path described.
U.K.: abbreviation of United Kingdom, attested from 1883.
U.N.: abbreviation of United Nations, attested from 1946.
ubeity (n.): "whereness," 1670s, from Modern Latin ubietas, from Latin ubi "where" (see ubi).
ubi: "place, location, position," 1610s, common in English c. 1640-1740, from Latin ubi "where?, in which place, in what place," relative pronominal adverb of place, ultimately from PIE *kwo-bhi- (source also of Sanskrit kuha, Old Church Slavonic kude "where"), locative case of pronominal base *kwo- (see who). Ubi sunt, literally "where are" (1914), in reference to lamentations for the mutability of things is from a phrase used in certain Medieval Latin Christian works.
ubiquitous (adj.): "being, existing, or turning up everywhere," 1800, from ubiquity + -ous. The earlier word was ubiquitary (c. 1600), from Modern Latin ubiquitarius, from ubique (see ubiquity). Related: Ubiquitously; ubiquitousness.
ubiquity (n.): "omnipresence," 1570s, from Modern Latin ubiquitas, from Latin ubique "everywhere," from ubi "where" (see ubi) + que "any, also, and, ever," as a suffix giving universal meaning to the word it is attached to, from PIE root *kwe "and." Originally a Lutheran theological position maintaining the omnipresence of Christ.
udder (n.): Old English udder "milk gland of a cow, goat, etc.," from Proto-Germanic *udr- (source also of Old Frisian uder, Middle Dutch uyder, Dutch uijer, Old High German utar, German Euter, and, with unexplained change of consonant, Old Norse jugr), from PIE *eue-dh-r "udder" (source also of Sanskrit udhar, Greek outhar, Latin uber "udder, breast").
UFO (n.): 1953, abbreviation of Unidentified Flying Object, which is attested from 1950.
ufology (n.): 1959, from UFO + -logy.
ug (v.): early 13c., "to inspire fear or loathing;" mid-14c. "to feel fear or loathing," from Old Norse ugga "to fear, dread" (see ugly). Related: Ugging.
Uganda: from Swahili u "land, country" + Ganda, indigenous people name, of unknown origin. Related: Ugandan.
Ugaritic: 1936, "pertaining to Ugarit," ancient city of northern Syria, and especially to the Semitic language first discovered there 1929 by Claude Schaeffer, from Ugarit, which probably is ultimately from Sumerian ugaru "field."
ugh: 1765, imitative of the sound of a cough; as an interjection of disgust, recorded from 1822.
uglification (n.): 1820 (Shelley), noun of action from uglify.
uglify (v.): 1570s; see ugly + -fy. Related: uglified; uglifying.
ugliness (n.): "repulsiveness of appearance," late 14c., from ugly + -ness.
ugly (adj.): mid-13c., uglike "frightful or horrible in appearance," from a Scandinavian source, such as Old Norse uggligr "dreadful, fearful," from uggr "fear, apprehension, dread" (perhaps related to agg "strife, hate") + -ligr "-like" (see -ly (1)). Meaning softened to "very unpleasant to look at" late 14c. Extended sense of "morally offensive" is attested from c. 1300; that of "ill-tempered" is from 1680s.

Among words for this concept, ugly is unusual in being formed from a root for "fear, dread." More common is a compound meaning "ill-shaped" (such as Greek dyseides, Latin deformis, Irish dochrud, Sanskrit ku-rupa). Another Germanic group has a root sense of "hate, sorrow" (see loath). Ugly duckling (1877) is from the story by Hans Christian Andersen, first translated from Danish to English 1846. Ugly American "U.S. citizen who behaves offensively abroad" is first recorded 1958 as a book title.
uh: inarticulate sound, attested from c. 1600; uh-huh, spoken affirmative (often ironic or non-committal) is recorded from 1904; negative uh-uh is attested from 1924.
UHF: 1937, abbreviation of ultra-high frequency (1932) in reference to radio frequencies in the range of 300 to 3,000 megahertz.
uhlan (n.): type of cavalryman, 1753, from German Uhlan, from Polish ułan "a lancer," from Turkish oghlan "a youth." For sense evolution, compare infantry.
uilleann: in uilleann pipe, from Irish uilleann "elbow," from Old Irish uilenn, from PIE *ol-ena-, from root *el- (1) "elbow, forearm" (see ell (n.1)).
ukase (n.): "decree issued by a Russian emperor," 1729, from Russian ukaz "edict," back-formation from ukazat' "to show, decree, to order," from Old Church Slavonic ukazati, from u- "away," perhaps here an intensive prefix, from PIE *au- (2) "off, away" + kazati "to show, order," from Slavic *kaz- (related to the first element of Casimir), from PIE root *kwek- "to appear, show."
uke (n.): short for ukulele, by 1915.
Ukraine: from Russian or Polish Ukraina, literally "border, frontier," from u- "at" + krai "edge." So called from being regarded as the southern frontier of Poland or Russia. Related: Ukrainian.
ukulele (n.): 1896, from Hawaiian 'ukulele, literally "leaping flea," from 'uku "louse, flea" + lele "to fly, jump, leap." Noted earlier in English as the Hawaiian word for "flea." The instrument so called from the rapid motion of the fingers in playing it. It developed from a Portuguese instrument introduced to the islands c. 1879.
ulcer (n.): c. 1400, from Old French ulcere, from Vulgar Latin ulcerem, from Latin ulcus (genitive ulceris) "ulcer, a sore," figuratively "painful subject," from PIE *elk-es- "wound" (source also of Greek elkos "a wound, sore, ulcer," Sanskrit Related: arsah "hemorrhoids").
ulceration (n.): c. 1400, from Latin ulcerationem (nominative ulceratio), noun of action from past participle stem of ulcerare "to make sore," from stem of ulcus (see ulcer).
ulcerous (adj.): early 15c., from Latin ulcerosus "full of sores," from stem of ulcus (see ulcer).
ulema (n.): "scholars of Muslim religious law," 1680s, from Arabic 'ulema "learned men, scholars," plural of 'alim "learned," from 'alama "to know."
ullage (n.): "amount by which a cask or bottle falls short of being full," late 15c., from Anglo-French ulliage (early 14c.), Anglo-Latin oliagium (late 13c.), Old French ouillage, from ouiller "to fill up (a barrel) to the bung," literally "to fill to the eye," from ueil "eye" (perhaps used colloquially for "bung"), from Latin oculus (see eye (n.)).
ulna (n.): inner bone of the forearm, 1540s, medical Latin, from Latin ulna "the elbow," also a measure of length, from PIE *el-ina-, extended form of root *el- (1) "elbow, forearm" (see ell (n.1)). Related: Ulnar.
Ulrich: masc. proper name, German, from Old High German Uodalrich, literally "of a rich home," from uodal "home, nobility" (related to Old English æðele "noble," Old Norse oðal "home").
Ulster: northernmost of the four provinces of Ireland, 14c., from Anglo-French Ulvestre (early 13c.), Anglo-Latin Ulvestera (c. 1200), corresponding to Old Norse Ulfastir, probably from Irish Ulaidh "men of Ulster" + suffix also found in Leinster, Munster, and perhaps representing Irish tir "land."
ult.: see ultimo.
ulterior (adj.): 1640s, "on the other side of," from Latin ulterior "more distant, more remote, farther, on the farther side," comparative of *ulter "beyond" (see ultra-). The sense "not at present in view or consideration" (as in ulterior motives) is attested from 1735.
ultimate (adj.): 1650s, from Late Latin ultimatus, past participle of ultimare "to be final, come to an end," from Latin ultimus (fem. ultima) "last, final, farthest, most distant, extreme," superlative of *ulter "beyond" (see ultra-). As a noun from 1680s. Ultimate Frisbee is attested by 1972.
ultimatum (n.): "final demand," 1731, from Modern Latin, from Medieval Latin ultimatum "a final statement," noun use of Latin adjective ultimatum "last possible, final," neuter of ultimatus (see ultimate). The Latin plural ultimata was used by the Romans as a noun, "what is farthest or most remote; the last, the end." In slang c. 1820s, ultimatum was used for "the buttocks."
ultimo (adv.): "in the month preceding the present," 1610s, common in abbreviated form ult. in 18c.-19c. correspondence and newspapers, from Latin ultimo (mense) "of last (month)," ablative singular masc. of ultimus "last" (see ultimate). Earlier it was used in the sense of "on the last day of the month specified" (1580s). Contrasted with proximo "in the next (month)," from Latin proximo (mense).
ultra vires: Latin, literally "beyond powers," from ultra (see ultra-) + vires "strength, force, vigor, power," plural of vis (see vim). Usually "beyond the legal or constitutional power of a court, etc."
ultra-: word-forming element meaning "beyond" (ultraviolet) or "extremely" (ultramodern), from Latin ultra- from ultra (adv. and prep.) "beyond, on the other side, on the farther side, past, over, across," from PIE *ol-tero-, suffixed form of root *al- (1) "beyond" (see alias (adv.)). In common use from early 19c., it appears to have arisen from French political designations. As its own word, a noun meaning "extremist" of various stripes, it is first recorded 1817, from French ultra, shortening of ultra-royaliste "extreme royalist."
ultra-conservative (adj.): 1828, from ultra- + conservative (adj.).
ultralight (adj.): 1959, from ultra- + light (adj.1). As a noun meaning "ultralight aircraft" it is recorded by 1979.
ultramarine (n.): 1590s, "blue pigment made from lapis lazuli," from Medieval Latin ultramarinus, literally "beyond the sea," from ultra- "beyond" + marinus "of the sea" (see marine (adj.)). Said to be so called because the mineral was imported from Asia.
ultramontane (adj.): 1590s, from Middle French ultramontain "beyond the mountains" (especially the Alps), from Old French (early 14c.), from Latin ultra "beyond" (see ultra-) + stem of mons (see mount (n.1)). Used especially of papal authority, though "connotation varies according to the position of the speaker or writer." [Weekley]
ultranationalism (n.): also ultra-nationalism, 1845, from ultra- + nationalism. Related: Ultranationalist
ultrasonic (adj.): "having frequency beyond the audible range," 1923, from ultra- + sonic. For sense, see supersonic.