U, 21st letter of the alphabet, corresponding to the Greek upsilon [Gr., = u without the aspirate]. Until the late Middle Ages the capital was V, the minuscule u, no distinction being made between the consonantal and vocalic uses of the letter. The fixing of modern orthography, however, has restricted u to the vowel, v to the consonant. In phonetics ŭ usually represents a high back rounded vowel, rather like ŏ in foot; English ū is a triphthong of y, ŏ, and w as in utensil; the Continental ū, or ō, is a diphthong of ŏ and w, as in glue. In chemistry, U is the symbol of the element uranium.