From The Collaborative International Dictionary of English v.0.48 [gcide]: 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.]