foursome

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A group of four persons or things, especially two couples.
• noun An activity involving four people, such as a golf match.

from The Century Dictionary.

• By fours; with four: said of anything in which four act together:
• noun A golf match in which four persons engage, two playing against the other two.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Scot. or Golf Consisting of four; requiring four participants.
• noun (Golf) 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.
• noun A group of four people or objects.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A group of four, a quartet or a game (such as golf) played by four players, especially by two teams of two.
• noun A fourgie, sex between four people

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun four people considered as a unit
• noun the cardinal number that is the sum of three and one