The Collaborative International Dictionary of English v.0.48:

Wilt \Wilt\, v. i. [imp. & p. p. Wilting.] [Written also welt,
   a modification of welk.]
   To begin to wither; to lose freshness and become flaccid, as
   a plant when exposed when exposed to drought, or to great
   heat in a dry day, or when separated from its root; to
   droop;. to wither. [Prov. Eng. & U. S.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

wilting
    n 1: causing to become limp or drooping [syn: wilt, wilting]