1530s, "social intercourse;" 1580s, "interchange of goods or property, trade," especially trade on a large scale by transportation between countries or different parts of the same country, from French commerce (14c.), from Latin commercium "trade, trafficking," from com "with, together" (see com-) + merx (genitive mercis) "merchandise" (see market (n.)). It also was the name of a card game very popular in 1770s and '80s. As a verb, "have dealings with," 1590s. Related: Commerced, commercing.
"relating to trade or commerce; pertaining to merchants," c. 1400, from merchant (n.) and from Old French marcheant (adj.).
"a professional person, one who follows a trade or occupation in a professional way," 1798, from professional (adj.).