Source : Webster's Revised Unabridged Dictionary (1913)

Circus \Cir"cus\, n.; pl. {Circuses}. [L. circus circle, ring,
   circus (in sense 1). See {Circle}, and cf. {Cirque}.]
   1. (Roman Antiq.) A level oblong space surrounded on three
      sides by seats of wood, earth, or stone, rising in tiers
      one above another, and divided lengthwise through the
      middle by a barrier around which the track or course was
      laid out. It was used for chariot races, games, and public
      shows.

   Note: The Circus Maximus at Rome could contain more than
         100,000 spectators. --Harpers' Latin Dict.

   2. A circular inclosure for the exhibition of feats of
      horsemanship, acrobatic displays, etc. Also, the company
      of performers, with their equipage.

   3. Circuit; space; inclosure. [R.]

            The narrow circus of my dungeon wall. --Byron.

Source : WordNet®

circus
     n 1: a travelling company of entertainers; including trained
          animals; "he ran away from home to join the circus"
     2: performance given by a traveling company of acrobats clowns
        and trained animals; "the children always love to go to
        the circus"
     3: a frenetic disorganized (and often comic) disturbance
        suggestive of a circus or carnival; "it was so funny it
        was a circus"; "the whole occasion had a carnival
        atmosphere" [syn: {carnival}]
     4: (antiquity) an open-air stadium for chariot races and
        gladiatorial games
     5: an arena consisting of an oval or circular area enclosed by
        tiers of seats and usually covered by a tent; "they used
        the elephants to help put up the circus"
     6: a genus of haws comprising the harriers [syn: {genus Circus}]