The Collaborative International Dictionary of English v.0.48:

Polity \Pol"i*ty\, n.; pl. Polities. [L. politia, Gr. ?: cf.
   F. politie. See 1st Policy, Police.]
   1. The form or constitution of the civil government of a
      nation or state; the framework or organization by which
      the various departments of government are combined into a
      systematic whole. --Blackstone. Hooker.
      [1913 Webster]

   2. Hence: The form or constitution by which any institution
      is organized; the recognized principles which lie at the
      foundation of any human institution.
      [1913 Webster]

            Nor is possible that any form of polity, much less
            polity ecclesiastical, should be good, unless God
            himself be author of it.              --Hooker.
      [1913 Webster]

   3. Policy; art; management. [Obs.] --B. Jonson.
      [1913 Webster]

   Syn: Policy.

   Usage: Polity, Policy. These two words were originally
          the same. Polity is now confined to the structure of a
          government; as, civil or ecclesiastical polity; while
          policy is applied to the scheme of management of
          public affairs with reference to some aim or result;
          as, foreign or domestic policy. Policy has the further
          sense of skillful or cunning management.
          [1913 Webster]

WordNet (r) 3.0 (2006):

polity
    n 1: the form of government of a social organization [syn:
         civil order, polity]
    2: a politically organized unit
    3: shrewd or crafty management of public affairs; "we was
       innocent of stratagems and polity"