Source : Webster's Revised Unabridged Dictionary (1913)

Pocketknife \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.

Source : WordNet®

pocketknife
     n : a knife with a blade that folds into the handle; suitable
         for carrying in the pocket [syn: {pocket knife}]
     [also: {pocketknives} (pl)]