The Collaborative International Dictionary of English v.0.48:

Reciprocity \Rec`i*proc"i*ty\ (r[e^]s`[i^]*pr[o^]s"[i^]*t[y^]),
   n. [Cf. F. r['e]ciprocit['e]. See Reciprocal.]
   1. Mutual action and reaction.
      [1913 Webster]

   2. Reciprocal advantages, obligations, or rights;
      reciprocation.
      [1913 Webster]

   Reciprocity treaty, or Treaty of reciprocity, a treaty
      concluded between two countries, conferring equal
      privileges as regards customs or charges on imports, or in
      other respects.
      [1913 Webster]

   Syn: Reciprocation; interchange; mutuality.
        [1913 Webster]

WordNet (r) 3.0 (2006):

reciprocity
    n 1: a relation of mutual dependence or action or influence
         [syn: reciprocality, reciprocity]
    2: mutual exchange of commercial or other privileges