class Aves vs order Podicipediformes

class Aves and order Podicipediformes both are nouns.

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

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