coliseum vs amphitheatre

coliseum and amphitheatre both are nouns.

Word	Noun	Adjective	Verb	Adverb
coliseum	Yes	No	No	No
amphitheatre	Yes	No	No	No

As nouns, coliseum and amphitheatre are synonyms defined as:

coliseum and amphitheatre: an oval large stadium with tiers of seats; an arena in which contests and spectacles are held

Other synonyms of coliseum include amphitheater.

coliseum (noun)	amphitheatre (noun)
an oval large stadium with tiers of seats; an arena in which contests and spectacles are held	an oval large stadium with tiers of seats; an arena in which contests and spectacles are held
	a sloping gallery with seats for spectators (as in an operating room or theater)