mid-15c., "act or business of grinding (grain) in a mill," verbal noun from mill (v.1). In reference to shaping metals by 1610s; in coin-making by 1817.
"one who grinds grain in a mill," mid-14c. (as a surname by early 14c.), agent noun from mill (v.1). In Middle English both with and without the -n-. The Old English word was mylnweard, literally "mill-keeper" (preserved in surname Millward, which is attested from late 13c.).
"one of a pair of cylindrical stones used in a mill for grinding grain," Middle English millestone, milne-ston, mullestone, from Old English mylenstan, from mill (n.1) + stone (n.). Compare Dutch molensteen, German Mühlstein, Danish møllesten. Figurative sense of "a burden" (1787) is from Matthew xviii.6.