What does "saponin" mean?

Saponin: 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 amorphus powder, which occasions a soapy lather in solution, and produces a local anæstesia. Formerly called also struthiin, quilaiin, senegin, polygalic acid, etc. By extension, any one of a group of related bodies of which saponin proper is the type.