The Collaborative International Dictionary of English v.0.48:

Imbrute \Im*brute"\, v. t. [imp. & p. p. Imbruted; p. pr. &
   vb. n. Imbruting.] [Pref. im- in + brute: cf. F. abrutir.
   Cf. Embrute.]
   To degrade to the state of a brute; to make brutal.
   [1913 Webster]

         And mixed with bestial slime,
         THis essence to incarnate and imbrute.   --Milton.
   [1913 Webster]