WordNet (r) 3.0 (2006):

Big Brother
    n 1: an authoritarian leader and invader of privacy
    2: an older brother

Moby Thesaurus II by Grady Ward, 1.0:

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