Definition of: u, U

(y) noun plural u's, U's or Us (yz)
1. The twenty-first letter of the English alphabet: from Greek upsilon. In Roman it was written V and had both consonant and vowel value. In English U was formerly the uncial or cursive form of V; gradually V came to be preferred in initial position in writing, and, as the sound at the beginning of a word is ordinarily consonantal, U was finally restricted to vowel use.
2. Any sound of the letter u. See ALPHABET.
—symbol
1. Chem. Uranium (symbol U).
2. Anything shaped like a U.