THREESOME definition: 1. three people as a group: 2. an act of three people having sex together: 3. a golf match for…. Learn more. Threesomes will not fix problems in your relationship. In fact, if there are deeply ignored problems in your relationship, a threesome may only serve to complicate those issues. The threesome ... A ménage à trois (French: [menaʒ a tʁwɑ]) is a domestic arrangement or committed relationship consisting of three people in polyamorous romantic or sexual relations with each other, and often dwelling together. [1][2] The phrase is a loan from French meaning " household of three ". Here, sex educators share the best positions for three -way oral sex, hand sex, mutual masturbation, double penetration, and everything in between.