'dealer' ultimately comes from Old English and Germanic roots related to dividing and distributing, formed in English with the agent suffix '-er' to mean 'one who deals or distributes.'

'dealer' developed from Old English dǣlan (to divide, distribute) through Middle English forms such as delen, with the agentive suffix '-er' added to form 'dealer' in later Middle English.

Initially it meant 'one who divides or distributes'; over time the sense narrowed and shifted toward 'one who trades, sells, or transacts' and specialized senses (e.g., card dealer, drug dealer, market dealer) developed.