The Collaborative International Dictionary of English v.0.48:

maltreat \mal*treat"\ (m[a^]l*tr[=e]t"), v. t. [imp. & p. p.
   Maltreated; p. pr. & vb. n. Maltreating.] [Mal- + treat:
   cf. F. maltraiter.]
   To treat ill; to abuse; to treat roughly.
   [1913 Webster]