class Aves vs order Pelecaniformes

class Aves and order Pelecaniformes both are nouns.

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

class Aves (noun)	order Pelecaniformes (noun)
(ornithology) the class of birds	pelicans, frigate birds, gannets, cormorants