Source : Webster's Revised Unabridged Dictionary (1913)

Knap \Knap\, n. [AS. cn[ae]p, cn[ae]pp, top, knob, button; cf.
   Icel. knappr knob, Sw. knapp, Dan. knap button, W., Gael., &
   Ir. cnap knob, button, and E. knop.]
   A protuberance; a swelling; a knob; a button; hence, rising
   ground; a summit. See {Knob}, and {Knop}.

         The highest part and knap of the same island.
                                                  --Holland.

Knap \Knap\, v. t. [imp. & p. p. {Knapped}; p. pr. & vb. n.
   {Knapping}.] [D. knappen to chew, bite, crack, take hold of;
   prob. of imitative origin.]
   1. To bite; to bite off; to break short. [Obs. or Prov. Eng.
      ]

            He will knap the spears apieces with his teeth.
                                                  --Dr. H. More.

            He breaketh the bow, and knappeth the spear in
            sunder.                               --Ps. xlvi. 9
                                                  (Book of
                                                  Common
                                                  Prayer.)

   2. To strike smartly; to rap; to snap. --Bacon.

Knap \Knap\, v. i.
   To make a sound of snapping. --Wiseman.

Knap \Knap\, n.
   A sharp blow or slap. --Halliwell.

Source : WordNet®

knap
     v 1: strike sharply; "rap him on the knuckles" [syn: {rap}]
     2: break a small piece off from; "chip the glass"; "chip a
        tooth" [syn: {chip}, {cut off}, {break off}]
     [also: {knapping}, {knapped}]