The Collaborative International Dictionary of English v.0.48:

Knap \Knap\, n.
   A sharp blow or slap. --Halliwell.
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The Collaborative International Dictionary of English v.0.48:

Knap \Knap\, v. i.
   To make a sound of snapping. --Wiseman.
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The Collaborative International Dictionary of English v.0.48:

Knap \Knap\ (n[a^]p), 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.
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         The highest part and knap of the same island.
                                                  --Holland.
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The Collaborative International Dictionary of English v.0.48:

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.
      ]
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            He will knap the spears apieces with his teeth.
                                                  --Dr. H. More.
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            He breaketh the bow, and knappeth the spear in
            sunder.                               --Ps. xlvi. 9
                                                  (Book of
                                                  Common
                                                  Prayer.)
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   2. To strike smartly; to rap; to snap. [Chiefly Brit.]
      --Bacon.
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WordNet (r) 3.0 (2006):

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