What does monger mean in the context of fishmonger?

The word "monger" in "fishmonger" refers to a person who sells a particular type of goods. In this case, a fishmonger is someone who sells fish. Other examples of "-monger" occupations include greengrocer (a person who sells fruits and vegetables), cheesemonger (a person who sells cheese), and ironmonger (a person who sells hardware and household goods).