class Aves vs order Rheiformes

class Aves and order Rheiformes both are nouns.

Word	Noun	Adjective	Verb	Adverb
class Aves	Yes	No	No	No
order Rheiformes	Yes	No	No	No

class Aves (noun)	order Rheiformes (noun)
(ornithology) the class of birds	a ratite bird order: birds intermediate in characteristics between ostriches and emus: recent and extinct rheas