working class vs stratum

working class and stratum both are nouns.

Word	Noun	Adjective	Verb	Adverb
working class	Yes	No	No	No
stratum	Yes	No	No	No

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

working class: a social class comprising those who do manual labor or work for wages
stratum: people having the same social, economic, or educational status

Other hypernyms of working class include class, social class, socio-economic class.

working class (noun)	stratum (noun)
a social class comprising those who do manual labor or work for wages	an abstract place usually conceived as having depth
	a subpopulation divided into a stratified sampling
	people having the same social, economic, or educational status
	one of several parallel layers of material arranged one on top of another (such as a layer of tissue or cells in an organism or a layer of sedimentary rock)