The Collaborative International Dictionary of English v.0.48:

Ballroom \Ball"room`\, n.
   A room for balls or dancing.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ballroom
    n 1: large room used mainly for dancing [syn: ballroom, dance
         hall, dance palace]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "ballroom":
   amusement park, cabaret, cafe chantant, cafe dansant, casino,
   chamber, chambre, dance floor, dance hall, dancery,
   dancing pavilion, entertainment industry, fun-fair, grand ballroom,
   juke joint, night spot, nightclub, nitery, resort, roadhouse, room,
   rotunda, salle, show biz, show business, tavern, theater