col·i·se·um also col·os·se·um (kŏl'ĭ-sē'əm) n. A large amphitheater for public sports events, entertainment, or assemblies.
[Medieval Latin Colisēum, an amphitheater in Rome, Italy, variant of Latin Colossēum, from neuter of colossēus, gigantic, from colossus, huge statue; see colossus.]