The Collaborative International Dictionary of English v.0.48:

Priesthood \Priest"hood\, n.
   1. The office or character of a priest; the priestly
      function. --Bk. of Com. Prayer.
      [1913 Webster]

   2. Priests, taken collectively; the order of men set apart
      for sacred offices; the order of priests.
      [1913 Webster]

WordNet (r) 3.0 (2006):

priesthood
    n 1: the body of ordained religious practitioners

The Jargon File (version 4.4.7, 29 Dec 2003):

priesthood
 n.

    [TMRC; obs.] The select group of system managers responsible for the
    operation and maintenance of a batch computer system. On these computers, a
    user never had direct access to a computer, but had to submit his/her data
    and programs to a priest for execution. Results were returned days or even
    weeks later.