diner vs eatery

diner and eatery both are nouns.

Word	Noun	Adjective	Verb	Adverb
diner	Yes	No	No	No
eatery	Yes	No	No	No

As nouns, eatery is a hypernym of diner; that is, eatery is a word with a broader meaning than diner:

Other hypernyms of diner include eating house, eating place, restaurant.

diner (noun)	eatery (noun)
a passenger car where food is served in transit	a building where people go to eat
a restaurant that resembles a dining car
a person eating a meal (especially in a restaurant)