membership

faithful, fold

collective, commune, community, cooperative

alliance, bloc, camp, coalition, partnership

body, cadre, group

circle, clan, clique, coterie, junta, junto, klatch (also klatsch), lot, set

crew, outfit, party, squad, team

branch, chapter, local

sisterhood, sorority

cabal, camarilla, camorra, confederacy, conspiracy

band, gang, ring

cartel, combine, syndicate

association, board, brotherhood, chamber, club, college, congress, consortium, council, fellowship, fraternity, guild (also gild), institute, institution, league, order, organization, society, sodality

count

class, roster

enrollment (also enrolment), registry

affiliation, alliance, association, collaboration, confederation, connection, cooperation, hookup, liaison, linkup, partnership, relation, relationship, tie-up, union

business, dealings, interaction

exchange, interconnection, interrelation, mutualism, reciprocity, symbiosis

incorporation, integration, merger, unification

affinity, attachment, closeness, intimacy, rapport, sympathy

kinship, oneness, solidarity, togetherness, unity

colleagueship, companionship, company, fellowship

bed, cahoots, league