four·some 
(fôrsəm)
(fôrsəm)n.
1. A group of four persons or things, especially two couples.
2. An activity involving four people, such as a golf match.
[Middle English four-som, from Old English fēowra sum, one of four : fēowra, genitive pl. of fēower, four; see FOUR + sum, one; see -SOME2.]