Source : Webster's Revised Unabridged Dictionary (1913)

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

Source : WordNet®

misspell
     v : spell incorrectly
     [also: {misspelt}]