The Collaborative International Dictionary of English v.0.48:

clannishness \clan"nish*ness\ n.
   1. a tendency to associate with only a select group.

   Syn: cliquishness, exclusiveness.
        [WordNet 1.5]

   2. a tendency to associate with only one's own clan; the
      propensity to display the sentiments, habits, and
      prejudices of one's own clan.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Clannish \Clan"nish\, a.
   Of or pertaining to a clan; closely united, like a clan;
   disposed to associate only with one's clan or clique;
   actuated by the traditions, prejudices, habits, etc., of a
   clan. -- Clan"nish*ly, adv. -- clan"nish*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

clannishness
    n 1: tendency to associate with only a select group [syn:
         clannishness, cliquishness, exclusiveness]