u

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The 21st letter of the modern English alphabet.
2. n. Any of the speech sounds represented by the letter u.
3. n. The 21st in a series.
4. n. Something shaped like the letter U.
5. n. A grade that indicates an unsatisfactory status.
6. abbr. up quark

Century Dictionary and Cyclopedia

1. An abbreviation [l. c] in a ship's log-book, of ugly threatening weather; [l. c] of uncle; of Unionist.
2. n. An abbreviation of United Brethren; of United Brethren in Christ.
3. n. An abbreviation of University College; of Upper Canada; of the Latin urbis conditæ, from the founding of the city, moaning from the first year of Rome.
4. An abbreviation of underproof, as applied to alcoholic liquors.
5. n. An abbreviation of Uncle Sam
6. n. of United Service
7. n. [lowercase or cap.] of the Latin ut supra, as above.
8. The twenty-first character and fifth vowel-sign in the English alphabet. The Phenician alphabet, from which ours comes ultimately (see under A), had no such sign, but ended with T. A sign for the u-sound (that is, for oo, or ö, as it is represented in the respellings of this dictionary) was added by the Greeks when they adapted the Phenician signs to their own use, and was written indifferently V or Y; but the latter finally established itself as the accepted form in Greek usage, while the former became customary in the derived Italian alphabets; so that, considerably later, the Romans were able to import Y as a separate and foreign character, to represent the foreign Greek sound ü (= French u, German ü or ue), into which the Greek ö had meanwhile become to a great extent altered in pronunciation. The V was also commonly written with its angle rounded, as U; and V and U were for a long time merely different forms of the same sign (like I and J): it is only recently that they have come to be always distinctly held apart, and have different values given them. As W also is a doubled U or V, it appears that our four letters U, V, W, and Y all come from a single sign added by the Greeks at the end of the Phenician system. The sound originally and properly represented by the character, and still belonging to it in most languages outside of English, is the oo or o sound, as in mood, move, rule, and the like, the closest of the labial vowels, or rounded vowels, as they are often called (see under O); but this value the letter has in English only in exceptional cases. What we call “long u,” namely, is this same sound with the semivowel y prefixed, as yoo (yo); and what we call “short u” is the more open of the two shades of neutral vowel-sound. The digraphs ue, eu, and ew also have, as long, the yo-value in the same manner and degree. The y-element in the sound, namely, is not always alike full and undeniable, but varies somewhat, according to the difficulty of slipping it in after a preceding consonant. After a guttural (k, q) or a labial (p, b, m, f, v), as when initial, the utterance is completely yö; but after the tongue-tip letters (t, d, n, th, s, z, l, r) the insertion of y involves a more difficult combination of movements of the tongue, and the element is apt to be slighted, being reduced rather to a bit of ł; and in the practice of many speakers, and in certain localities, it is even omitted altogether, so that the yö becomes simple ö, new being pronounced noo, lurid loorid, and so on. The difficulty in the way of inserting the y, however, is removed if the preceding syllable has the accent; and hence even those who pronounce penö'rious say pen'ū ry, and so in all other like cases. This omission of the y-element is not approved, but is stigmatized as provincial or vulgar, although practised by many educated and careful speakers, and probably becoming more prevalent. It is more generally condoned, and even accepted, after l than after t, d, n, etc., and some standard authorities in England itself now prononnce and teach lö instead of lū ; in this dictionary the u is so marked if it occurs after l preceded by another consonant, as in fluid (flo-id). After r, the difficulty of adding the y-sound before a vowel is greater than after any other tongue-tip consonant; hence in this situation the pronunciation of “long u” as ö is almost universally accepted and practised. Further, after t, d, s, z, “long u” becomes o when the y-element is as it were absorbed into them, converting them (see the different letters) into ch, j, sh, and zh; nor is the y-element heard when ū follows any of these sounds having an independent origin, as in jury, etc. The real short u-sound, or that corresponding to ö as long, is in a limited number of words also represented by u, as in bull, put, etc.; also by double o, as in look, foot, etc. What we call “short u” is in the great majority of cases written with u, but also with o, as in son, with oo, as in blood, and with ou, as in young, and in the slighted pronunciation of unaccented syllables with almost any vowel. Cases like bury and busy and buy are anomalous and isolated. A u is always written after q, and this u (save in the exceptional cases in which it is silent) has a consonantal value, being pronounced as the semivowel w; and it is so treated sometimes also after other consonants, especially s, as in suave, persuade, anguish. U is silent in many words after g, having only (as in French) the office of preserving the hard sound of the g; thus, guide, plague. Like i and y, u is never doubled.
9. As a symbol: The chemical symbol of uranium.
10. In quaternions, an operational sign which, prefixed to the symbol of a quaternion, denotes the versor of that quaternion.
11. In the theory of heat, a symbol used to denote the energy, or the sum of the increment of heat and the heat consumed.
12. [lowercase] In the calculus, the symbol of a function.
13. [lowercase] In hydrodynamics, used with v and w to denote the rectangular components of the velocity.
14. n. An abbreviation of Italian una corda, on one string.
15. n. An abbreviation of United Kingdom (of Great Britain and Ireland).
16. n. An abbreviation of United Presbyterian.
17. n. An abbreviation of United States (of America).

Wiktionary

1. n. The twenty-first letter of the basic modern Latin alphabet.
2. n. metrology symbol for unified atomic mass unit
3. n. phonetics Used in the International Phonetic Alphabet and in several romanization systems of non-Latin scripts to represent a close back rounded vowel (IPA: /u/).
4. n. The twenty-first letter of the English alphabet, called u and written in the Latin script.
5. n. The name of the Latin script letter U/u.
6. n. A thing in the shape of the letter U
7. pro. abbreviation, slang, text messaging, Internet you (in text messaging and internet conversations)
8. abbr. Underwater.

GNU Webster's 1913

1. the twenty-first letter of the English alphabet, is a cursive form of letter V, with which it was formerly used interchangeably, both letters being then used both as vowels and consonants. U and V are now, however, differentiated, U being used only as a vowel or semivowel, and V only as a consonant. The true primary vowel sound of U, in Anglo-Saxon, was the sound which it still retains in most of the languages of Europe, that of long oo, as in tool, and short oo, as in wood, answering to the French ou in tour. Etymologically U is most closely related to o, y (vowel), w, and v; as in two, duet, dyad, twice; top, tuft; sop, sup; auspice, aviary. See v, also o and y.

WordNet 3.0

1. adj. (chiefly British) of or appropriate to the upper classes especially in language use
2. n. a base containing nitrogen that is found in RNA (but not in DNA) and derived from pyrimidine; pairs with adenine
3. n. a heavy toxic silvery-white radioactive metallic element; occurs in many isotopes; used for nuclear fuels and nuclear weapons
4. n. the 21st letter of the Roman alphabet