U (named u , plural ues"U", Oxford English Dictionary, 2nd edition (1989); Merriam-Webster's Third New International Dictionary of the English Language, Unabridged (1993)Brown & Kiddle (1870) The institutes of English grammar, page 19.
Ues is the plural of the name of the letter; the plural of the letter itself is rendered U's, Us, u's, or us.) is the 21st letter and the fifth vowel in the ISO basic Latin alphabet. It is preceded by T, and is followed by V.
During the late Middle Ages, two forms of 'v' developed, which were both used for its ancestor 'u' and modern 'v'. The pointed form 'v' was written at the beginning of a word, while a rounded form 'u' was used in the middle or end, regardless of sound. So whereas 'valour' and 'excuse' appeared as in modern printing, 'have' and 'upon' were printed 'haue' and 'vpon', respectively. The first recorded use of 'u' and 'v' as distinct letters is in a Gothic alphabet from 1386, where 'v' preceded 'u'. Printers eschewed capital 'U' into the 17th century and the distinction between the two letters was not fully accepted by the French Academy until 1762.
The letter is used in the digraphs , (various pronunciations, but usually /aʊ/), and with the value of "long u" in , , and in a few words (as in 'fruit'). It often has the sound before a vowel in the sequences (as in 'quick'), (as in 'anguish'), and (as in 'suave'), though it is silent in final -que (as in 'unique') and in many words with (as in 'guard').
One thing to note is that certain varieties of the English language (i.e. British English, Canadian English, etc.) use the letter U in words such as colour, labour, valour, etc.; however, in American English the letter is not used and said words mentioned are spelled as color and so on.
In French orthography the letter represents the close front rounded vowel (); is represented by . In Dutch and Afrikaans, it represents either , or a near-close near-front rounded vowel (); likewise the phoneme is represented by . In Welsh orthography the letter can represent a long close front unrounded vowel () or short near-close near-front unrounded vowel () in Southern dialects. In Northern dialects, the corresponding long and short vowels are a long close central unrounded vowel () and a short lowered close central unrounded vowel (), respectively. and are represented by .
'u' is the symbol for the atomic mass unit and 'U' is the symbol for one Enzyme unit.
In IPA, the close back rounded vowel is represented by the lower case ⟨u⟩.
U is also the source of the mathematical symbol ∪, representing a union. It is used mainly for and geometry.
It is used as for micro- in metric measurements as a replacement for the Greek letter μ (mu), of which it is a graphic approximation, when that Greek letter is not available, as in "um" for μm (micrometer).
Some universities, such as the University of Miami and the University of Utah, are locally known as "The U".