gentry vs upper crust

gentry and upper crust both are nouns.

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

As nouns, upper crust is a hypernym of gentry; that is, upper crust is a word with a broader meaning than gentry:

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

Other hypernyms of gentry include upper class.

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