1.A relationship involving three people, especially one in which three people live together and have sexual relations, such as a married couple and a lover of one of the pair.
2.A single sexual encounter in which three people participate.
3.(figurative) An unlikely situation in which a group of three people not normally associated with each other participate in an activity together. " For the first time in World Championships history, two racers shared the first-place gold medal. Maier and Kjus arm-in-arm on the podium, with Austrian Hans Knauss just.01 seconds back from making it a menage-a-trois."
