'colosseum-like' originates from Latin and Old English/Proto-Germanic: the element 'colosseum' comes from Latin 'Colosseum' (via Italian 'Colosseo') ultimately from Greek 'kolossos', where 'kolossos' meant 'giant statue'; the suffix '-like' comes from Old English 'līc' (Proto-Germanic *-līkaz), meaning 'having the form of'.

'colosseum' changed from Latin 'Colosseum' (the name of the Roman amphitheatre, itself named after a nearby 'colossus' statue) into Middle English and then modern English 'Colosseum'; the adjectival suffix developed from Old English 'līc' into Modern English '-like', producing the compound form 'colosseum-like'.

Initially, 'Colosseum' referred specifically to the great amphitheatre in Rome; over time, combining it with '-like' produced a descriptive adjective meaning 'resembling that amphitheatre' or more broadly 'monumental/amphitheater-like' in appearance.