/ ˌmeɪnɑːʒ ɑː ˈtrwʌ/ noun
( pl. ménages à trois / ˌmeɪnɑːʒ ɑː ˈtrwʌ/) [ usually sing. ] (from French ) a situation where three people, especially a husband, wife and lover, live together and have sexual relationships with each other
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WORD ORIGIN
French , household of three .