bitternut

from WordNet (r) 3.0 (2006)

bitternut
    n 1: hickory of the eastern United States having a leaves with 7
         or 9 leaflets and thin-shelled very bitter nuts [syn:
         {bitternut}, {bitternut hickory}, {bitter hickory}, {bitter
         pignut}, {swamp hickory}, {Carya cordiformis}]

from The Collaborative International Dictionary of English v.0.48

Bitternut \Bit"ter*nut"\, n. (Bot.)
   The swamp hickory ({Carya amara}). Its thin-shelled nuts are
   bitter.
   [1913 Webster]