• (British) IPA: /ˈθɹiːsəm/

threesome (plural threesomes)

1. A group of three people or things.
2. An instance of sexual activity involving three people.
   • 2013, Joanna Biggs, "Tell me everything", London Review of Books, vol. 35, no. 7:

     ‘Tell me everything,’ she said to Losse, and when she’d heard everything, got the colleague who kept suggesting a threesome discreetly demoted.

   • 2016, John Oliver, “Charter Schools”, in Last Week Tonight with John Oliver, season 3, episode 22, written by Tim Carvell; Josh Gondelman; Dan Gurewitch; Jeff Maurer; Ben Silva; Will Tracy; Jill Twiss; Seena Vali; Julie Weiner, HBO, Warner Bros. Television:

     That’s a threesome joke about her fucking children! It was in the first season and they gave her another one!

• (group of three people) triad, trine, trinity, trio, troika, triumvirate; see also Thesaurus:trio
• (sexual activity) ménage à trois, troilism

• twosome, foursome, fivesome, etc.
• moresome

• French: trio
• Italian: trio
• Portuguese: trio
• Russian: тро́е
• Spanish: trío

• French: plan à trois, triolisme, ménage à trois
• German: Dreier
• Portuguese: ménage à trois, ménage, encontro à três
• Russian: триоли́зм
• Spanish: trío