a poisonous glucoside found in many plants, as in the root of soapwort (saponaria), in the bark of soap bark (quillaia), etc. it is extracted as a white amorphous powder, which occasions a soapy lather in solution, and produces a local anaesthesia. formerly called also struthiin, quillaiin, senegin, polygalic acid, etc. by extension, any one of a group of related bodies of which saponin proper is the type.