U, or u, the twentieth letter and fifth vowel of our alphabet, is formed in the voice by a round configuration of the lips, and a greater extrusion of the under one than in forming the letter o. The sound is short in curst, rust, tun, tub; but is lengthened by a final e, as in tune, ule, &c. In some words it is rather acute than long; as brute, flute, lute, &c. It is mostly long in polysyllables; as in union, curious, &c.; but in some words it is obscure, as in nature, venture, &c.