lunchroom vs restaurant

lunchroom and restaurant both are nouns.

Word	Noun	Adjective	Verb	Adverb
lunchroom	Yes	No	No	No
restaurant	Yes	No	No	No

As nouns, restaurant is a hypernym of lunchroom; that is, restaurant is a word with a broader meaning than lunchroom:

Other hypernyms of lunchroom include eatery, eating house, eating place.

lunchroom (noun)	restaurant (noun)
a restaurant (in a facility) where lunch can be purchased	a building where people go to eat