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®

soapberry tree
     n : a tree of the genus Sapindus whose fruit is rich in saponin
         [syn: {soapberry}]