Source : Webster's Revised Unabridged Dictionary (1913)

Soapberry tree \Soap"ber`ry tree`\ (Bot.)
   Any tree of the genus {Sapindus}, esp. {Sapindus saponaria},
   the fleshy part of whose fruit is used instead of soap in
   washing linen; -- also called {soap tree}.

Source : WordNet®

Sapindus saponaria
     n : evergreen of tropical America having pulpy fruit containing
         saponin which was used as soap by native Americans [syn:
         {China tree}, {false dogwood}, {jaboncillo}, {chinaberry}]