The Collaborative International Dictionary of English v.0.48:

Prefect \Pre"fect\, n. [L. praefectus, fr. praefectus, p. p. of
   praeficere to set over; prae before + facere to make: cf. F.
   pr['e]fet.]
   1. A Roman officer who controlled or superintended a
      particular command, charge, department, etc.; as, the
      prefect of the aqueducts; the prefect of a camp, of a
      fleet, of the city guard, of provisions; the pretorian
      prefect, who was commander of the troops guarding the
      emperor's person.
      [1913 Webster]

   2. A superintendent of a department who has control of its
      police establishment, together with extensive powers of
      municipal regulation. [France] --Brande & C.
      [1913 Webster]

   3. In the Greek and Roman Catholic churches, a title of
      certain dignitaries below the rank of bishop.
      [1913 Webster]

   Apostolic prefect (R. C. Ch.), the head of a mission, not
      of episcopal rank. --Shipley.
      [1913 Webster]

WordNet (r) 3.0 (2006):

prefect
    n 1: a chief officer or chief magistrate; "the prefect of Paris
         police"

Moby Thesaurus II by Grady Ward, 1.0:

47 Moby Thesaurus words for "prefect":
   apprentice teacher, archon, auditor, autodidact, chancellor,
   chief executive, chief executive officer, dean, educatee,
   executive, executive director, executive officer,
   executive secretary, graduate assistant, inquirer, intern, learner,
   magistrate, management, managing director, monitor, officer,
   official, paraprofessional, practice teacher, praepostor,
   president, prexy, proctor, provost, pupil, pupil teacher, scholar,
   secretary, self-taught person, student, student assistant, studier,
   teaching assistant, teaching fellow, teaching intern,
   the administration, trainee, treasurer, vice-chancellor,
   vice-president, warden



Bouvier's Law Dictionary, Revised 6th Ed (1856):

PREFECT, French law. A chief officer invested with the superintendence of
the administration of the laws in each department. Merl. Repert. h.t.