The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bitterwood \Bit"ter*wood`\, n.
   A West Indian tree (Picr[ae]na excelsa) from the wood of
   which the bitter drug Jamaica quassia is obtained.
   [1913 Webster]