class Aves vs order Aepyorniformes

class Aves and order Aepyorniformes both are nouns.

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

class Aves (noun)	order Aepyorniformes (noun)
(ornithology) the class of birds	huge extinct flightless birds: elephant birds