amphitheatre vs Australian spelling

amphitheatre and Australian spelling both are nouns.

Word	Noun	Adjective	Verb	Adverb
amphitheatre	Yes	No	No	No
Australian spelling	Yes	No	No	No

amphitheatre (noun)	Australian spelling (noun)
an oval large stadium with tiers of seats; an arena in which contests and spectacles are held	English orthography used in Australia (characterized by 'analyse', 'centre', 'usable')
a sloping gallery with seats for spectators (as in an operating room or theater)