mill-pond n.

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 machinery for manufacturing" is from c. 1500. In old slang also "a typewriter" (1913); "a boxing match or other pugilistic bout" (1819).

c. 1300 (by mid-13c. in compounds, c. 1200 in surnames, possibly in Old English), "artificially banked body of water," variant of pound "enclosed place" (for livestock, etc.; see pound (n.2)). Applied locally to natural pools and small lakes from late 15c. Jocular use in reference to the Atlantic Ocean dates from 1640s. Pond scum "free-floating freshwater algae" (Spirogyra) is from 1864 (also called frog-spittle and brook-silk; as figurative for "someone extremely repulsive," it is attested from 1984.