middle class vs stratum

middle class and stratum both are nouns.

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

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

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

middle class (noun)	stratum (noun)
the social class between the lower and upper classes	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)