The Collaborative International Dictionary of English v.0.48:

Dementate \De*men"tate\, a. [L. dementatus, p. p. See Dement,
   v. t.]
   Deprived of reason.
   [1913 Webster]

         Arise, thou dementate sinner!            --Hammond.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Dementate \De*men"tate\v. t.
   To deprive of reason; to dement. [R.] --Burton.
   [1913 Webster]