amphitheatre vs sports stadium

amphitheatre and sports stadium both are nouns.

Word	Noun	Adjective	Verb	Adverb
amphitheatre	Yes	No	No	No
sports stadium	Yes	No	No	No

As nouns, sports stadium is a hypernym of amphitheatre; that is, sports stadium is a word with a broader meaning than amphitheatre:

amphitheatre: an oval large stadium with tiers of seats; an arena in which contests and spectacles are held
sports stadium: a large structure for open-air sports or entertainments

Other hypernyms of amphitheatre include arena, bowl, stadium.

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