ménage à trois
/meɪˈnɑːʒɑːˈtrwɑː/noun
(pl. ménages à trois 读音同)
- an arrangement in which three people live or have a relationship together, typically a married couple and the lover of one of them（尤指结婚双方和第三者）三角关系; 三人苟合。
词源
French, 'household of three'.