Princeton's WordNet

1. circus(noun)

   a travelling company of entertainers; including trained animals

   Synonyms:
   carnival, genus Circus

2. circus(noun)

   a performance given by a traveling company of acrobats, clowns, and trained animals

   Synonyms:
   carnival, genus Circus

3. circus, carnival(noun)

   a frenetic disorganized (and often comic) disturbance suggestive of a large public entertainment

   Synonyms:
   fair, funfair, circus, carnival, genus Circus

4. circus(noun)

   (antiquity) an open-air stadium for chariot races and gladiatorial games

   Synonyms:
   carnival, genus Circus

5. circus(noun)

   an arena consisting of an oval or circular area enclosed by tiers of seats and usually covered by a tent

   Synonyms:
   carnival, genus Circus

6. Circus, genus Circus(noun)

   a genus of haws comprising the harriers

   Synonyms:
   carnival, genus Circus