saponin \sap"onin\, n. l. sapo, -onis soap: cf. f. saponine.
   chem.
   a poisonous glucoside found in many plants, as in the root of
   soapwort saponaria officinalis, in the bark of soap bark
   quillaja saponaria, etc. it is extracted as a white
   amorphous powder, which produces a soapy lather in solution,
   and produces a local anaesthesia. it is used as a detergent
   and for emulsifying oils. 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.
   1913 webster + pjc
see also:
saponaria officinalis quillaja saponaria struthiin quillaiin senegin polygalic acid