The Collaborative International Dictionary of English v.0.48:

Misspell \Mis*spell"\, v. t. [imp. & p. p. Misspelled, or
   Misspelt; p. pr. & vb. n. Misspelling.]
   To spell incorrectly.
   [1913 Webster]

WordNet (r) 3.0 (2006):

misspell
    v 1: spell incorrectly