Webster’s Revised Unabridged Dictionary · 1913 Coliseum Col′i·se′um, n. [NL. (cf. It. coliseo, colosseo), fr. L. colosseus colossal, fr. colossus a colossus. See Colossus, and cf. Colosseum.] The amphitheater of Vespasian at Rome, the largest in the world. [Written also Colosseum.] ‹ Colin Colitis ›