ménage à trois

noun2

1. •
   A household or relationship whereby three people live together as lovers.

   • Old men frequently marry young girls, but then the portion is high and the ménage à trois common. — 1856
2. •
   A sexual act or experience involving three people; a threesome.

   • David and Angela and I had a ménage à trois for about five minutes, but then I made her leave because David and I were gonna play. — 1996