fair sex vs class

fair sex and class both are nouns.

Word	Noun	Adjective	Verb	Adverb
fair sex	Yes	No	No	No
class	Yes	No	Yes	No

As nouns, class is a hypernym of fair sex; that is, class is a word with a broader meaning than fair sex:

Other hypernyms of fair sex include social class, socio-economic class, stratum.

fair sex (noun)	class (noun)
women as a class	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

fair sex (verb)	class (verb)
	arrange or order by classes or categories