key out vs class

key out is not a noun while class is a noun.

Word	Noun	Adjective	Verb	Adverb
key out	No	No	Yes	No
class	Yes	No	Yes	No

key out (noun)	class (noun)
	education imparted in a series of lessons or meetings
	elegance in dress or behavior
	a collection of things sharing a common attribute
	people having the same social, economic, or educational status
	(biology) a taxonomic group containing one or more orders
	a body of students who are taught together
	a body of students who graduate together
	a league ranked by quality

key out (verb)	class (verb)
identify as in botany or biology, for example	arrange or order by classes or categories