amphitheatre vs amphitheatrical

amphitheatre is a noun but amphitheatrical is not a noun.

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

amphitheatre (noun)	amphitheatrical (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)

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