class Aves vs order Piciformes

class Aves and order Piciformes both are nouns.

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

class Aves (noun)	order Piciformes (noun)
(ornithology) the class of birds	woodpeckers, jacamars, puffbirds, barbets, honey guides, toucans