The Collaborative International Dictionary of English v.0.48:

Episcopacy \E*pis"co*pa*cy\, n. [See Episcopate.]
   Government of the church by bishops; church government by
   three distinct orders of ministers -- bishops, priests, and
   deacons -- of whom the bishops have an authority superior and
   of a different kind.
   [1913 Webster]

WordNet (r) 3.0 (2006):

episcopacy
    n 1: the collective body of bishops [syn: episcopacy,
         episcopate]