trader vs merchant

trader and merchant both are nouns.

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

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

trader: someone who purchases and maintains an inventory of goods to be sold
merchant: a businessperson engaged in retail trade

Other hypernyms of trader include merchandiser.

trader (noun)	merchant (noun)
someone who purchases and maintains an inventory of goods to be sold	a businessperson engaged in retail trade