Source : Webster's Revised Unabridged Dictionary (1913)

Knife \Knife\, n.; pl. {Knives}. [OE. knif, AS. cn[=i]f; akin to
   D. knijf, Icel. kn[=i]fr, Sw. knif, Dan. kniv.]
   1. An instrument consisting of a thin blade, usually of steel
      and having a sharp edge for cutting, fastened to a handle,
      but of many different forms and names for different uses;
      as, table knife, drawing knife, putty knife, pallet knife,
      pocketknife, penknife, chopping knife, etc..

   2. A sword or dagger.

            The coward conquest of a wretch's knife. --Shak.

   {Knife grass} (Bot.) a tropical American sedge ({Scleria
      latifolia}), having leaves with a very sharp and hard
      edge, like a knife.

   {War to the knife}, mortal combat; a conflict carried to the
      last extremity.

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

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

Knife \Knife\, v. t.
   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.]

Source : WordNet®

knife
     n 1: edge tool used as a cutting instrument; has a pointed blade
          with a sharp edge and a handle
     2: a weapon with a handle and blade with a sharp point
     3: any long thin projection that is transient; "tongues of
        flame licked at the walls"; "rifles exploded quick knives
        of fire into the dark" [syn: {tongue}]
     [also: {knives} (pl)]

knife
     v : use a knife on; "The victim was knifed to death" [syn: {stab}]
     [also: {knives} (pl)]