"one engaged in the business of buying commercial commodities and selling them again for profit," early 13c., marchaunt (late 12c. as a surname), from Anglo-French marchaunt "merchant, shopkeeper" (Old French marcheant, Modern French marchand), from Vulgar Latin *mercatantem (nominative *mercatans) "a buyer," present participle of *mercatare, frequentative of Latin mercari "to trade, traffic, deal in" (see market (n.)). Meaning "fellow, chap" is from 1540s; with a specific qualifier, and suggesting someone who deals in it (such as speed merchant "one who enjoys fast driving," by 1914).
"relating to trade or commerce; pertaining to merchants," c. 1400, from merchant (n.) and from Old French marcheant (adj.).