The Collaborative International Dictionary of English v.0.48:

Disestablishment \Dis`es*tab"lish*ment\, n.
   1. The act or process of unsettling or breaking up that which
      has been established; specifically, the withdrawal of the
      support of the state from an established church; as, the
      disestablishment and disendowment of the Irish Church by
      Act of Parliament.
      [1913 Webster]

   2. The condition of being disestablished.
      [1913 Webster]

WordNet (r) 3.0 (2006):

disestablishment
    n 1: the act terminating an established state of affairs;
         especially ending a connection with the Church of England