The Collaborative International Dictionary of English v.0.48:

Molt \Molt\, Moult \Moult\, v. i. [imp. & p. p. Molted or
   Moulted; p. pr. & vb. n. Molting or Moulting.] [OE.
   mouten, L. mutare. See Mew to molt, and cf. Mute, v. t.]
   [The prevalent spelling is, perhaps, moult; but as the u
   has not been inserted in the otherwords of this class, as,
   bolt, colt, dolt, etc., it is desirable to complete the
   analogy by the spelling molt.]
   To shed or cast the hair, feathers, skin, horns, or the like,
   as an animal or a bird. --Bacon.
   [1913 Webster] Molt

The Collaborative International Dictionary of English v.0.48:

U \U\ ([=u]),
   the twenty-first letter of the English alphabet, is a cursive
   form of the letter V, with which it was formerly used
   interchangeably, both letters being then used both as vowels
   and consonants. U and V are now, however, differentiated, U
   being used only as a vowel or semivowel, and V only as a
   consonant. The true primary vowel sound of U, in Anglo-Saxon,
   was the sound which it still retains in most of the languages
   of Europe, that of long oo, as in tool, and short oo, as in
   wood, answering to the French ou in tour. Etymologically U is
   most closely related to o, y (vowel), w, and v; as in two,
   duet, dyad, twice; top, tuft; sop, sup; auspice, aviary. See
   V, also O and Y.
   [1913 Webster] See Guide to Pronunciation, [sect][sect]
   130-144.
   [1913 Webster]

WordNet (r) 3.0 (2006):

u
    adj 1: (chiefly British) of or appropriate to the upper classes
           especially in language use
    n 1: a base containing nitrogen that is found in RNA (but not in
         DNA) and derived from pyrimidine; pairs with adenine [syn:
         uracil, U]
    2: a heavy toxic silvery-white radioactive metallic element;
       occurs in many isotopes; used for nuclear fuels and nuclear
       weapons [syn: uranium, U, atomic number 92]
    3: the 21st letter of the Roman alphabet [syn: U, u]