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
2. Any place of public contest or exertion; any sphere of
action; as, the arenaof debate; the arena of life.
3. (Med.) "Sand" or "gravel" in the kidneys.