dealer vs costermonger

dealer and costermonger both are nouns.

Word	Noun	Adjective	Verb	Adverb
dealer	Yes	No	No	No
costermonger	Yes	No	No	No

As nouns, costermonger is a hyponym of dealer; that is, costermonger is a word with a more specific, narrower meaning than dealer:

dealer: someone who purchases and maintains an inventory of goods to be sold
costermonger: a hawker of fruit and vegetables from a barrow

dealer (noun)	costermonger (noun)
a firm engaged in trading	a hawker of fruit and vegetables from a barrow
a seller of illicit goods
the person who distributes the playing cards in a card game
someone who purchases and maintains an inventory of goods to be sold
the major party to a financial transaction at a stock exchange; buys and sells for his own account