(1):
(n.) 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.
(2):
(n.) Any place of public contest or exertion; any sphere of action; as, the arenaof debate; the arena of life.
(3):
(n.) "Sand" or "gravel" in the kidneys.