order Rheiformes vs class Aves

order Rheiformes and class Aves both are nouns.

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

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