amphitheatre vs coliseum

amphitheatre and coliseum both are nouns.

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

As nouns, amphitheatre and coliseum are synonyms defined as:

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

Other synonyms of amphitheatre include amphitheater.

amphitheatre (noun)	coliseum (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)