Noted yesterday: the innovation throuple (based on couple), to describe a romantic or sexual threesome, triple, or triad.
(Hat tip to Will Parsons.)
In my household, we called ourselves a (married) triple.
Throuple appears to be pretty recent, though those things are hard to judge. A few cites:
Check out this new movie from filmmaker Cayle Ryan Pietras about a “throuple” – three gay men in a relationship. (link)
In my first “throuple” and loving it (link) [woman and two men]
What It’s Like to Be In a Three-Way Relationship (aka a “Throuple”)
A “throuple” is when three people date each other, all at the same time. (link) [man and two women]
Yes, three-woman throuples do occur, but I haven’t been able to google up any good cites.