The Collaborative International Dictionary of English v.0.48:

Goa powder \Go"a pow"der\ [So called from Goa, on the Malabar
   coast, whither it was shipped from Portugal.]
   A bitter powder (also called araroba) found in the
   interspaces of the wood of a Brazilian tree (Andira
   araroba) and used as a medicine. It is the material from
   which chrysarobin is obtained.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Goa powder
    n 1: a bitter yellow powder used to treat skin diseases [syn:
         araroba, Goa powder, chrysarobin]