Middle English mille, "building fitted to grind grain," Old English mylen "a mill" (10c.), an early Germanic borrowing from Late Latin molina, molinum "mill" (source of French moulin, Spanish molino), originally fem. and neuter of molinus "pertaining to a mill," from Latin mola "mill, millstone," related to molere "to grind," from PIE root *mele- "to crush, grind." The -n- gradually was lost in English but survives in the surname Milner. Also from Late Latin molina, directly or indirectly, are German Mühle, Old Saxon mulin, Old Norse mylna, Danish mølle, Old Church Slavonic mulinu.
The meaning "mechanical device for grinding grain for food" is from 1550s. The broader sense of "machine for grinding or pulverizing any solid substance" is attested from 1670s. Other types of manufacturing machines driven by wind or water, that transform raw material by a process other than grinding began to be called mills by early 15c. Sense of "large building fitted with industrial machinery for manufacturing" is from c. 1500. In old slang also "a typewriter" (1913); "a boxing match or other pugilistic bout" (1819).
"one-tenth of a cent," 1786, an original U.S. currency unit but now used only for tax calculation purposes, shortening of Latin millesimum "one-thousandth part," from mille "a thousand" (see million). Formed on the analogy of cent, which is short for Latin centesimus "one hundredth" (of a dollar). Compare mil.
1550s, "subject to mechanical operations carried on in a mill;" 1560s, "to grind in or as in a mill, reduce to fine particles;" from mill (n.1). Meaning "to flute the edge (of a coin, etc.) is from 1724. Related: milled; milling.
"to keep moving round and round without purpose in a mass," 1874 (originally of cattle, implied in milling), originally of cattle, from mill (n.1) on resemblance to the action of a mill wheel. Related: Milled.