black market n.

Old English blæc "absolutely dark, absorbing all light, of the color of soot or coal," from Proto-Germanic *blakaz "burned" (source also of Old Norse blakkr "dark," Old High German blah "black," Swedish bläck "ink," Dutch blaken "to burn"), from PIE *bhleg- "to burn, gleam, shine, flash" (source also of Greek phlegein "to burn, scorch," Latin flagrare "to blaze, glow, burn"), from root *bhel- (1) "to shine, flash, burn." The usual Old English word for "black" was sweart (see swart).

The same root produced Middle English blake "pale," from Old English blac "bright, shining, glittering, pale;" the connecting notions being, perhaps, "fire" (bright) and "burned" (dark), or perhaps "absence of color." According to OED, in Middle English "it is often doubtful whether blac, blak, blake, means 'black, dark,' or 'pale, colourless, wan, livid' "; and the surname Blake can mean either "one of pale complexion" or "one of dark complexion."  

Black was used of dark-skinned people in Old English. Of coffee with nothing added, attested by 1796. The meaning "fierce, terrible, wicked" is from late 14c. The figurative senses often come from the notion of "without light," moral or spiritual. Latin niger had many of the same figurative senses ("gloomy; unlucky; bad, wicked, malicious"). The metaphoric use of the Greek word, melas, however, tended to reflect the notion of "shrouded in darkness, overcast." In English it has been the color of sin and sorrow at least since c. 1300; the sense of "with dark purposes, malignant" emerged 1580s (in black art "necromancy;" it is also the sense in black magic). 

Black drop (1823) was a liquid preparation of opium, used medicinally. Black-fly (c. 1600) was a name given to various insects, especially an annoying pest of the northern American woods. Black Prince as a nickname of the eldest son of Edward III is attested by 1560s; the exact signification is uncertain. Black flag, flown (especially by pirates) as a signal of no mercy, is from 1590s. Black dog "melancholy" is attested from 1826.

Black belt is from 1870 in reference to district extending across the U.S. South with heaviest African population (also sometimes in reference to the fertility of the soil); it is attested from 1913 in the judo sense, worn by one who has attained a certain high degree of proficiency. Black power is from 1966, associated with Stokely Carmichael. Black English "English as spoken by African-Americans," is by 1969. The Black Panther (1965) movement was an outgrowth of Student Nonviolent Co-ordinating Committee. Black studies is attested from 1968.

early 12c., "a meeting at a fixed time for buying and selling livestock and provisions, an occasion on which goods are publicly exposed for sale and buyers assemble to purchase," from Old North French market "marketplace, trade, commerce" (Old French marchiet, Modern French marché), from Latin mercatus "trading, buying and selling; trade; market" (source of Italian mercato, Spanish mercado, Dutch markt, German Markt), from past participle of mercari "to trade, deal in, buy," from merx (genitive mercis) "wares, merchandise." This is from an Italic root *merk-, possibly from Etruscan, referring to various aspects of economics.

The god Mercurius was probably the god of exchange. According to [Walde-Hoffmann], the god's name was borrowed from Etruscan; in principle, the same is possible for the stem *merk- altogether. [de Vaan]

Meaning "public building or space where markets are held" is attested from late 13c. Meaning "a city, country or region considered as a place where things are bought or sold" is from 1610s. Sense of "sale as controlled by supply and demand" is from 1680s. Market-garden "plot of land on which vegetables are grown for market" is by 1789. Market-basket "large basket used to carry marketing" is by 1798. Market price "price a commodity will bring when sold in open market" is from mid-15c.; market value "value established or shown by sales" (1690s) is first attested in the writings of John Locke. Market economy is from 1948; market research is from 1921.