WordNet (r) 3.0 (2006):

sorority
    n 1: a social club for female undergraduates

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "sorority":
   affiliation, alignment, alliance, amalgamation, association,
   boon companionship, brotherhood, brotherliness, cahoots, chumship,
   club, coadunation, coalescence, coalition, colleagueship,
   collegialism, collegiality, combination, community of interest,
   companionship, comradeship, confederacy, confederation,
   confraternity, confrerie, consolidation, consortship,
   copartnership, copartnery, country club, esprit de corps,
   federation, fellowship, fraternal order, fraternalism, fraternity,
   fraternization, freemasonry, fusion, guild, hookup, inclusion,
   incorporation, integration, league, merger, order, partnership,
   secret society, sisterhood, sisterliness, society, sodality,
   tie-in, tie-up, unification, union