Saponin \Sap"o*nin\, n. [L. sapo, -onis soap: cf. F. saponine.]

(Chem.) 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 an[ae]sthesia. 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.

Source: Webster's Revised Unabridged Dictionary (1913)