sap·o·nin 
(săpə-nĭn, sə-pō-)
(săpə-nĭn, sə-pō-)n.
Any of various plant glycosides that form soapy lathers when mixed and agitated with water, used in detergents, foaming agents, and emulsifiers.
[From Latin sāpō, sāpōn-, hair dye, of Germanic origin.]