D defs.my
Entry 3 senses Webster, 1913

ménage à trois

/(mā̇`nȧzh" ȧ trwȧ)/ · mé·nage à· trois · IPA /ˌmeɪnɑːʒ ɑː ˈt(ɹ)wɑː/
01 n. A relationship involving three people, especially one in which three people live together and have sexual relations, such as a married coup…
  1. 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. 2.
    A single sexual encounter in which three people participate.
  3. 3.
    An unlikely situation in which a group of three people not normally associated with each other participate in an activity together.[figurative]
    “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.” — Andrew Hood, in (http://classic.mountainzone.com/ski/worldcup/99/worldchamps/superg-m.html)