cohabit
v.
euphemism since 1530s to describe a couple living together without benefit of marriage; back-formation from cohabitation. Related: Cohabited; cohabiting.
〔李〕[co-;habit] n.（男女）同居； 姘居 ←habit,hibit (L habere,habitum)=to have or hold 拥有，占有
〔蒋〕[co-共同，habit居住] (男女)同居，姘居