The Collaborative International Dictionary of English v.0.48:

Inseparability \In*sep`a*ra*bil"i*ty\, n. [L. inseparabilitas:
   cf. F. ins['e]parabilit['e].]
   The quality or state of being inseparable; inseparableness.
   --Locke.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "inseparability":
   accretion, adherence, adhesion, agglomeration, agglutination,
   cling, clinging, clotting, clustering, coagulation, coherence,
   cohesion, cohesiveness, compaction, concretion, condensation,
   congealment, congelation, conglobation, conglomeration,
   consolidation, impartibility, indiscerptibility, indissolubility,
   indivisibility, infrangibility, infusibility, insolubility,
   junction, set, solidification, sticking, unity