WordNet (r) 3.0 (2006):

P.A. system
    n 1: an electronic amplification system used as a communication
         system in public areas [syn: public address system, P.A.
         system, PA system, P.A., PA]

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "PA system":
   Gramophone, PA, Victrola, audio sound system, audiophile,
   binaural system, bitch box, bullhorn, cartridge, ceramic pickup,
   changer, crystal pickup, derived four-channel system,
   discrete four-channel system, four-channel stereo system, hi-fi,
   hi-fi fan, high-fidelity, intercom, intercommunication system,
   jukebox, magnetic pickup, monaural system, mono, needle,
   nickelodeon, phonograph, photoelectric pickup, pickup,
   public-address system, quadraphonic sound system,
   radio-phonograph combination, record changer, record player,
   sound reproduction system, sound truck, squawk box, stereo, stylus,
   system, tape deck, tape recorder, tone arm,
   transcription turntable, turntable