Source : Webster's Revised Unabridged Dictionary (1913)

Mistaught \Mis*taught"\, a. [See {Misteach}.]
   Wrongly taught; as, a mistaught youth. --L'Estrange.

Misteach \Mis*teach"\, v. t. [imp. & p. p. {Mistaught}; p. pr. &
   vb. n. {Misteaching}.] [AS. mist?can.]
   To teach wrongly; to instruct erroneously.