Source : Webster's Revised Unabridged Dictionary (1913)

Pignut \Pig"nut\, n. (Bot.)
   (a) See {Groundnut}
   (d) .
   (b) The bitter-flavored nut of a species of hickory ({Carya
       glabra, or porcina}); also, the tree itself.

Source : WordNet®

pignut
     n : an American hickory tree having bitter nuts [syn: {pignut
         hickory}, {brown hickory}, {black hickory}, {Carya glabra}]