order Casuariiformes vs class Aves

order Casuariiformes and class Aves both are nouns.

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

order Casuariiformes (noun)	class Aves (noun)
a ratite bird order: cassowaries and emus	(ornithology) the class of birds