cosurfactant
noun
co·sur·fac·tant (ˌ)kō-(ˌ)sər-ˈfak-tənt 
(ˌ)kō-ˈsər-ˌfak-tənt
variants or co-surfactant
plural cosurfactants or co-surfactants
: a chemical substance that is used in addition to a surfactant to improve its performance
especially : a second surfactant that is used in conjunction with a primary surfactant
Word History
First Known Use
1970, in the meaning defined above