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).

The substitution of Middle English -o- for Old English -u- before -m-, -n-, or -r- was a French scribal habit before minims to avoid misreading the letters in the old style handwriting, which jammed them together. The practice transformed some, come, monk, tongue, worm.

German or Austrian subway system, 1938 (originally in reference to Berlin), from German U-bahn, short for Untergrund-bahn, literally "underground railway."

"whereness," 1670s, from Modern Latin ubietas, from Latin ubi "where" (see 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 root *kwo-. 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.

"omnipresence," 1570s, from Modern Latin ubiquitas, from Latin ubique "everywhere," from ubi "where" (see ubi) + -que "and," also "any, also, ever," as a suffix giving universal meaning to the word it is attached to, from PIE root *kwe "and, -ever" (source also of Hittite -kku "now, even, and;" Sanskrit -ca, Avestan -ca "and, also, if;" Greek -te "and;" Gothic -uh "and, also," nih "if not").

Originally a Lutheran theological position maintaining the omnipresence of Christ.

"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.

1916 (said to have been in use from 1913), partial translation of German U-Boot, short for Unterseeboot, literally "undersea boat."

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").

1953, abbreviation of Unidentified Flying Object, which is attested from 1950.

1959, from UFO + -logy.