any of various plant glucosides that form soapy lathers when mixed and agitated with water; used in detergents and foaming agents and emulsifiers
source: WordNet 3.0
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 anæsthesia. 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.