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

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "priesthood":
   Sacred College, apostleship, call, care of souls, clergy,
   clerical order, clericalism, clericals, episcopalianism,
   holy orders, ministry, pastorage, pastoral care, pastorate,
   prelacy, presbytery, priestery, priestism, priestship, rabbinate,
   sacerdotalism, sacred calling, the church, the cloth, the desk,
   the ministry, the pulpit, ultramontanism, vocation



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.