"reduction in price," 1880, from the verbal expression mark down "reduce in price" (1859), from mark (v.) in the sense of "put a numerical price on an object for sale" + down (adv.). Mark down as "make a note of" is by 1881.

"insult, snub," 1962, from verbal phrase put down "to snub," attested from c. 1400 in this sense, earlier (c. 1300) "to lower, let down," also (mid-14c.) "to throw down, reject;" see put (v.) + down (adv.). To put (something) down "end by force or authority" (a rebellion, etc.) is from mid-14c.  Compare set-down "a rebuff, a scolding" (1780).

"setback, sudden change for the worse in one's circumstances," 1840, from verbal phrase; see come (v.) + down (adv.). In 16c.-17c. "total destruction" was expressed metaphorically as "to come to Castle Comedown" (1560s).

also letdown, "a disappointment," 1768, from let (v.) + down (adv.). The verbal phrase is from mid-12c. in a literal sense "cause to be lowered," of drawbridges, etc.; figuratively by 1754.

also rub-down, "an act of rubbing down," by 1885, from verbal phrase, from rub (v.) + down (adv.).

1866, of persons, "to have the health or strength reduced," from the verbal phrase; see run (v.) + down (adv.). From 1896 of places, "dilapidated, shabby, seedy;" by 1894 of clocks, etc., "completely unwound." The earliest sense is "oppressed" (1680s). Compare rundown (n.).

The verbal phrase run down as "have the motive power exhausted" (of clocks, etc.) is by 1761; of persons, etc., "become weak or exhausted," by 1828. To run (something or someone) down "disparage, abuse" is by 1660s. 

also knockdown, 1680s, from the verbal phrase knock down, attested from mid-15c. in the sense "fell to the ground;" see knock (v.) + down (adv.). As a noun from 1809. Phrase knock-down, drag-out is from 1827.

late 15c., earlier upsadoun (late 14c.), up so down (c. 1300); the so perhaps meaning "as if." As an adjective from 1866.

in figurative sense of "withdraw a charge," 1859, American English, from the notion of descending a ladder, etc. (such a literal sense is attested by 1849); from back (v.) + down (adv.).

also low down, lowdown, "vulgar, far down the social scale," 1888, from low (adj.) + down (adv.). Earlier it had meant "humble" (1540s). As a noun, 1915, from the adjective, American English. Low-downer was late 19c. American English colloquial for "poor white; rude, mean person."