1.  foursome(n = noun.group) quartet, quartette - four people considered as a unit; "he joined a barbershop quartet"; "the foursome teed off before 9 a.m."
is a kind of assemblage, gathering
has particulars: quadrumvirate

2.  foursome(n = noun.quantity) 4, four, iv, little joe, quadruplet, quartet, quatern, quaternary, quaternion, quaternity, tetrad - the cardinal number that is the sum of three and one;
is a kind of digit, figure

   Consisting of four; requiring four participants. [Webster 1913 Suppl.]

1.  A game between four players, with two on each side and each side playing but one ball, the partners striking alternately. It is called a mixed foursome when each side consists of a man and a woman. [Webster 1913 Suppl.]

2.  A group of four people or objects; as, we need another player to make a foursome for bridge. [PJC]

foursome, n.
1 a group of four persons.
2 a golf match between two pairs with partners playing the same ball.