The Collaborative International Dictionary of English v.0.48:

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 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]

The Collaborative International Dictionary of English v.0.48:

Quillaia bark \Quil*la"ia bark`\ (Bot.)
   The bark of a rosaceous tree (Quillaja Saponaria), native
   of Chile. The bark is finely laminated, and very heavy with
   alkaline substances, and is used commonly by the Chileans
   instead of soap. Also called soap bark.
   [1913 Webster]