class Aves vs order Colymbiformes

class Aves and order Colymbiformes both are nouns.

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

class Aves (noun)	order Colymbiformes (noun)
(ornithology) the class of birds	grebes