The Collaborative International Dictionary of English v.0.48:

Circus \Cir"cus\, n.; pl. Circuses. [L. circus circle, ring,
   circus (in sense 1). See Circle, and cf. Cirque.]
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   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.
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   Note: The Circus Maximus at Rome could contain more than
         100,000 spectators. --Harpers' Latin Dict.
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   2. A circular inclosure for the exhibition of feats of
      horsemanship, acrobatic displays, etc. Also, the company
      of performers, with their equipage.
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   3. Circuit; space; inclosure. [R.]
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            The narrow circus of my dungeon wall. --Byron.
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