(n.) One who makes a bargain; -- sometimes in the sense of bargainer.

Greek affiliate associate bargainer belonger brother business agent card-carrier card-carrying member charter member clubber clubman clubwoman committeeman comrade conventioneer conventioner conventionist dues-paying member enlistee enrollee fellow fraternity man guildsman honorary member initiate insider joiner labor organizer life member member negotiator one of us organizer pledge shop steward sister socius sorority girl sorority woman trade unionist union member union officer unionist