class Aves vs order Struthioniformes

class Aves and order Struthioniformes both are nouns.

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

class Aves (noun)	order Struthioniformes (noun)
(ornithology) the class of birds	a ratite bird order: ostriches and related extinct birds; known from the Pleistocene onward