upper class vs gentry

upper class and gentry both are nouns.

Word	Noun	Adjective	Verb	Adverb
upper class	Yes	No	No	No
gentry	Yes	No	No	No

As nouns, gentry is a hyponym of upper class; that is, gentry is a word with a more specific, narrower meaning than upper class:

upper class: the class occupying the highest position in the social hierarchy
gentry: the most powerful members of a society

Other hyponyms of upper class include elite, elite group, aristocracy, people in power, ruling class.

upper class (noun)	gentry (noun)
the class occupying the highest position in the social hierarchy	the most powerful members of a society