china tree: evergreen of tropical America having pulpy fruit containing saponin which was used as soap by Native Americans
soapberry: a tree of the genus Sapindus whose fruit is rich in saponin
four-stroke engine: an internal-combustion engine in which an explosive mixture is drawn into the cylinder on the first stroke and is compressed and ignited on the second stroke; work is done on the third stroke and the products of combustion are exhausted on the fourth stroke