grocer vs merchant

grocer and merchant both are nouns.

Word	Noun	Adjective	Verb	Adverb
grocer	Yes	No	No	No
merchant	Yes	No	No	No

As nouns, merchant is a hypernym of grocer; that is, merchant is a word with a broader meaning than grocer:

grocer: a retail merchant who sells foodstuffs (and some household supplies)
merchant: a businessperson engaged in retail trade

Other hypernyms of grocer include merchandiser.

grocer (noun)	merchant (noun)
a retail merchant who sells foodstuffs (and some household supplies)	a businessperson engaged in retail trade