WordWeb Online

1. Characteristic of a clan especially in being unified
   "clannish loyalty"
    
2. Befitting or characteristic of those who incline to social exclusiveness and who rebuff the advances of people considered inferior
   "The group did not consider themselves to be clannish or unfriendly";
   - cliquish, clubby, snobbish, snobby

See also: joint, private

Encyclopedia: Clannish