The twenty-first letter of the modern English alphabet and the twentieth of the ancient Roman one, a differentiated form of the letter V. Latin manuscripts written in capitals have V only, but other Latin manuscripts also have a modified form of this, resembling u. Both forms occur in OE manuscripts: capital V represents either V or U, and the modified form usually represents the vowel u. In ME the symbols u and v both occur, but without formal distinction of use.
During the 16th century continental printers began to distinguish lower case u as the vowel symbol and v as the consonant symbol, and by the mid 17th century this was also the case in English. Capital V continued to be used for both V and U into the 17th century, but in the course of that century it was replaced, for the vowel, by capital U. From about 1700 the regular forms have been U u for the vowel, and V v for the consonant. However, many dictionaries continued into the 19th century to give items beginning with u or v in a single alphabetic sequence.
U is used (of language or social behaviour) to mean characteristic of or appropriate to the upper social classes. The expression is an abbreviation of upper class, and was coined in 1954 by Alan S. C. Ross, professor of linguistics, the term was popularized by its use in Nancy Mitford's Noblesse Oblige (1956).