The Collaborative International Dictionary of English v.0.48:

Fraternization \Fra`ter*ni*za"tion\ (? or ?), n.
   The act of fraternizing or uniting as brothers.
   [1913 Webster]

         I hope that no French fraternization . . . could so
         change the hearts of Englishmen.         --Burke.
   [1913 Webster]

WordNet (r) 3.0 (2006):

fraternization
    n 1: associating with others in a brotherly or friendly way;
         especially with an enemy [syn: fraternization,
         fraternisation]

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "fraternization":
   affiliation, alignment, alliance, amalgamation, association,
   cahoots, coadunation, coalescence, coalition, collaboration,
   colleagueship, collegialism, collegiality, combination,
   companionship, company, comradeship, confederacy, confederation,
   confraternity, consociation, consolidation, cooperation,
   copartnership, copartnery, federation, fellowship,
   fifth-column activity, fraternalism, fraternity, freemasonry,
   fusion, high treason, hookup, inclusion, incorporation,
   integration, league, lese majesty, membership, merger,
   misprision of treason, partaking, participation, partnership,
   petty treason, quislingism, sedition, sharing, society, sodality,
   sorority, tie-in, tie-up, treason, unification, union