"ordinary, unspectacular," 1922, a figurative use of a commercial phrase attested by 1909 in reference to material yielded by a mill (n.1), etc., before sorting for quality (compare common run "usual, ordinary type," from 1712). From run (n.) on the notion of "a continuous stretch of grinding."
Entries linking to run-of-the-mill
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).
mid-15c. (earlier ren, late 14c.), "a spell of running, the act of running," from run (v.).
The Old English noun ryne/yrn (early Middle English rine) meant "a flowing, a course, a watercourse;" the modern sense of "small stream" is recorded from 1580s, mostly in Northern English dialect and American English. The sense of "a flowing or pouring, as of liquid" is by 1814. In reference to the action of a school of fish moving together, especially upstream or in-shore, by 1820.
From 1804 as "place where anything runs or may run." The meaning "the privilege of going through or over, free access" is from 1755. In. U.S. baseball, "feat of running around the bases without being put out" by 1856; the sense in cricket is from 1746.
Meaning "continuous stretch" (of something) is from 1670s. That of "continuous use, circulation, or observance" (as in run of luck) is by 1714. The general sense of "a continuous series or succession" has yielded many specific meanings, as "three or more playing cards in consecutive order" (1870). In music, "a rapid succession of consecutive tones," by 1835.
The financial meaning "extraordinary series or rush of demands on a bank, etc." is recorded from 1690s. The market sense of "sustained demand for something" is by 1816.
From 1712 as "a spell of sailing between two ports;" hence also "an excursion trip" (1819); "single trip by a railroad train" (1857); the military aircraft attack sense (as in bombing run) is from 1916. Hence also "a regular round in a vehicle" (as in paper run, milk run, etc.).
In printing, the meaning "total number of copies done in a single period of press-work" is from 1909. In publishing, "set or series of consecutive numbers of a periodical," by 1889.
Meaning "tear in a knitted garment or stocking" is from 1922, probably on the notion of "a failure caused by looseness, weakness, or giving way;" to run had a specialized sense in reference to machinery, "to slip, go awry" (1846), and in reference to lace it meant "to unravel, come undone" (1878). Also compare running stitch "loose, open stitch" (1848).
Phrase a run for one's money "satisfaction for trouble taken" is from 1872 in a figurative sense, from horse racing, where it implied real competition (1841).