order Passeriformes vs class Aves

order Passeriformes and class Aves both are nouns.

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

order Passeriformes (noun)	class Aves (noun)
largest order of birds comprising about half the known species: rooks, finches, sparrows, tits, warblers, robins, wrens, swallows, etc.; the four suborders are Eurylaimi, Tyranni, Menurae and Oscines or Passeres	(ornithology) the class of birds