amphitheatrical vs amphitheater

amphitheatrical is not a noun while amphitheater is a noun.

Word	Noun	Adjective	Verb	Adverb
amphitheatrical	No	Yes	No	No
amphitheater	Yes	No	No	No

amphitheatrical (noun)	amphitheater (noun)
	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)

amphitheatrical (adjective)	amphitheater (adjective)
of or related to an amphitheater