class Aves vs order Podicipitiformes

class Aves and order Podicipitiformes both are nouns.

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

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