The Collaborative International Dictionary of English v.0.48:

Fat \Fat\, v. t. [imp. & p. p. Fatted; p. pr. & vb. n.
   atting.] [OE. fatten, AS. f[=ae]ttian. See Fat, a., and
   cf. Fatten.]
   To make fat; to fatten; to make plump and fleshy with
   abundant food; as, to fat fowls or sheep.
   [1913 Webster]

         We fat all creatures else to fat us.     --Shak.
   [1913 Webster]