retailer vs merchandiser

retailer and merchandiser both are nouns.

Word	Noun	Adjective	Verb	Adverb
retailer	Yes	No	No	No
merchandiser	Yes	No	No	No

As nouns, merchandiser is a hypernym of retailer; that is, merchandiser is a word with a broader meaning than retailer:

Other hypernyms of retailer include distributer, distributor, merchant.

retailer (noun)	merchandiser (noun)
a merchant who sells goods at retail	a businessperson engaged in retail trade