amphitheater vs amphitheatric

amphitheater is a noun but amphitheatric is not a noun.

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

amphitheater (noun)	amphitheatric (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)

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