A seller of eatables about the streets, properly an appleseller (from costard, a sort of apple, and monger, “a trader;” Saxon, mangian, “to trade”), a word still retained in iron-monger, cheese-monger, fish-monger, news-monger, fell-monger, etc.
“Her father was an Irish costarmonger.”
B. Jonson: The Alchemist, iv. 1.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894