The Collaborative International Dictionary of English v.0.48:

Overseer \O`ver*seer"\, n.
   One who oversees; a superintendent; a supervisor; as, an
   overseer of a mill; specifically, one or certain public
   officers; as, an overseer of the poor; an overseer of
   highways.
   [1913 Webster]

WordNet (r) 3.0 (2006):

overseer
    n 1: a person who directs and manages an organization [syn:
         overseer, superintendent]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "overseer":
   Big Brother, auditor, boatswain, boss, chief, comptroller,
   controller, floor manager, floorman, floorwalker, foreman, gaffer,
   ganger, head, headman, inspector, manager, monitor,
   noncommissioned officer, overman, proctor, sirdar, slave driver,
   straw boss, subforeman, super, superintendent, superior,
   supervisor, surveyor, taskmaster, visitor