WordNet (r) 3.0 (2006):

big top
    n 1: a canvas tent to house the audience at a circus
         performance; "he was afraid of a fire in the circus tent";
         "they had the big top up in less than an hour" [syn:
         circus tent, big top, round top, top]

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "big top":
   burlesque show, carnival, circus, coochie show, fantoccini,
   floor show, galanty show, girly show, hootchy-kootchy show,
   leg show, light show, magic show, ombres chinoises, peep show,
   puppet show, raree-show, rep show, repertory show, rodeo,
   shadow show, sideshow, the big top, variety show,
   vaudeville show