Quiz: Remember the definition of mal de mer?
late 14c., "path, track, course of action," introduced by the Hanse merchants, from Middle Dutch or Middle Low German trade "track, course" (probably originally of a trading ship), cognate with Old English tredan (see tread). Sense of "one's habitual business" (1540s) developed from the notion of "way, course, manner of life" (mid-15c.); sense of "buying and selling" is first recorded 1550s. Trade wind (1640s) has nothing to do with commerce, but preserves the obsolete sense of "in a habitual or regular course." Trade union is attested from 1831.
1540s, "to tread a path," from trade (n.). Meaning "to occupy oneself (in something)" is recorded from c.1600. The U.S. sports team sense of "to exchange one player for another" is attested from 1899. Related: Traded; trading. To trade down is attested from 1942. Trade-in in reference to used cars is recorded from 1917. Trading post is recorded from 1796.
Business or commerce; economic activity.