The Collaborative International Dictionary of English v.0.48:

Knife \Knife\, v. t. [imp. & p. p. Knifed; p. pr. & vb. n.
   Knifing.]
   1. (Hort.) To prune with the knife.
      [1913 Webster]

   2. To cut or stab with a knife. [Low]
      [1913 Webster]

   3. Fig.: To stab in the back; to try to defeat by underhand
      means, esp. in politics; to vote or work secretly against
      (a candidate of one's own party). [Slang, U. S.]
      [Webster 1913 Suppl.]