The Collaborative International Dictionary of English v.0.48:

Arena \A*re"na\, n.; pl. E. Arenas; L. Aren[ae]. [L. arena,
   harena, sand, a sandy place.]
   1. (Rom. Antiq.) The area in the central part of an
      amphitheater, in which the gladiators fought and other
      shows were exhibited; -- so called because it was covered
      with sand.
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   2. Any place of public contest or exertion; any sphere of
      action; as, the arenaof debate; the arena of life.
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   3. (Med.) "Sand" or "gravel" in the kidneys.
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