means A person who buys and sells financial instruments, goods, or assets — often for short-term profit — as their occupation.

from From the verb 'trade,' which entered English in the 1500s meaning a course or track one regularly follows, hence a habitual line of business. It comes from Middle Low German 'trade' meaning a track or course, a cousin of 'tread' — the path you walk repeatedly. So a trader is, at root, someone who walks the same well-worn route to market, again and again. The '-er' simply marks the doer.