The Collaborative International Dictionary of English v.0.48:

Prelacy \Prel"a*cy\, n.; pl. Prelacies. [LL. praelatia. See
   Prelate; cf. Prelaty.]
   1. The office or dignity of a prelate; church government by
      prelates.
      [1913 Webster]

            Prelacies may be termed the greater benefices.
                                                  --Ayliffe.
      [1913 Webster]

   2. The order of prelates, taken collectively; the body of
      ecclesiastical dignitaries. "Divers of the reverend
      prelacy, and other most judicious men." --Hooker.
      [1913 Webster]

WordNet (r) 3.0 (2006):

prelacy
    n 1: prelates collectively [syn: prelacy, prelature]
    2: the office or station of a prelate [syn: prelacy,
       prelature]