The Collaborative International Dictionary of English v.0.48:

Mutuality \Mu`tu*al"i*ty\, n. [Cf. F. mutualit['e].]
   1. The quality of correlation; reciprocation; interchange;
      interaction; interdependence.
      [1913 Webster]

   2. (Law) Reciprocity of consideration. --Wharton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mutuality
    n 1: a reciprocality of sentiments; "the mutuality of their
         affection was obvious" [syn: mutuality, mutualness]
    2: a reciprocal relation between interdependent entities
       (objects or individuals or groups) [syn: mutuality,
       interdependence, interdependency]

Moby Thesaurus II by Grady Ward, 1.0:

137 Moby Thesaurus words for "mutuality":
   accord, accordance, affinity, agape, agreement, alternation, amity,
   balance, battledore and shuttlecock, bipartisanship,
   bonds of harmony, brotherly love, caritas, cement of friendship,
   charity, coaction, coadjuvancy, coadministration, coagency,
   cochairmanship, codirectorship, coequality, collaboration,
   collaborativeness, collectivism, collusion, commensalism,
   common effort, common enterprise, communalism, communion,
   communism, communitarianism, community, community of interests,
   commutation, compatibility, complicity, concert, concord,
   concordance, concurrence, congeniality, cooperation,
   cooperativeness, corelation, correlation, correlativism,
   correlativity, correspondence, counterchange, cross fire, duet,
   duumvirate, ecumenicalism, ecumenicism, ecumenism, empathy,
   equilibrium, equipollence, equivalence, esprit, esprit de corps,
   exchange, feeling of identity, fellow feeling, fellowship,
   frictionlessness, give-and-take, good vibes, good vibrations,
   happy family, harmony, identity, interchange, intermutation,
   interplay, inverse proportion, inverse ratio, inverse relationship,
   joining of forces, joint effort, joint operation, kinship,
   lex talionis, like-mindedness, love, mass action,
   measure for measure, morale, mutual admiration, mutual assistance,
   mutual support, mutual transfer, mutualism, octet, oneness, peace,
   permutation, pooling, pooling of resources, proportionality,
   pulling together, quartet, quid pro quo, quintet, rapport,
   rapprochement, reciprocality, reciprocation, reciprocity,
   relativity, retaliation, septet, sextet, sharing, solidarity,
   something for something, symbiosis, symmetry, sympathy, symphony,
   synergism, synergy, team spirit, teamwork, tit for tat, transposal,
   transposition, trio, triumvirate, troika, understanding, union,
   unison, united action, unity