pock·et·knife /ˈpɑkətˌnaɪf/
  隨身小折刀
  Pock·et·knife n.; pl. -knives  A knife with one or more blades, which fold into the handle so as to admit of being carried in the pocket.
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  pocketknife
       n : a knife with a blade that folds into the handle; suitable
           for carrying in the pocket [syn: pocket knife]
       [also: pocketknives (pl)]