Source : Webster's Revised Unabridged Dictionary (1913)

Quassia \Quas"si*a\, n. [NL. From the name of a negro, Quassy,
   or Quash, who prescribed this article as a specific.]
   The wood of several tropical American trees of the order
   {Simarube[ae]}, as {Quassia amara}, {Picr[ae]na excelsa}, and
   {Simaruba amara}. It is intensely bitter, and is used in
   medicine and sometimes as a substitute for hops in making
   beer.

Source : WordNet®

Quassia amara
     n : handsome South American shrub or small tree having bright
         scarlet flowers and yielding a valuable fine-grained
         yellowish wood; yields the bitter drug quassia from its
         wood and bark [syn: {quassia}, {bitterwood}]