Old English blæc "dark," from Proto-Germanic *blakaz "burned" (cf. Old Norse blakkr "dark," Old High German blah "black," Swedish bläck "ink," Dutch blaken "to burn"), from PIE *bhleg- "to burn, gleam, shine, flash" (cf. Greek phlegein "to burn, scorch," Latin flagrare "to blaze, glow, burn"), from root *bhel- (1) "to shine, flash, burn;" see bleach (v.).
The same root produced Old English blac "bright, shining, glittering, pale;" the connecting notions being, perhaps, "fire" (bright) and "burned" (dark). The usual Old English word for "black" was sweart (see swart). According to OED: "In ME. it is often doubtful whether blac, blak, blake, means 'black, dark,' or 'pale, colourless, wan, livid.' " Used of dark-skinned people in Old English.
Of coffee, first attested 1796. Meaning "fierce, terrible, wicked" is late 14c. The color of sin and sorrow since at least c.1300; sense of "with dark purposes, malignant" emerged 1580s (e.g. black magic). Black face in reference to a performance style originated in U.S., is from 1868. Black flag, flown (especially by pirates) as a signal of "no mercy," from 1590s. Black dog "melancholy" attested from 1826. Black belt is from 1875 in reference to districts of the U.S. South with heaviest African population; 1870 with reference to fertility of soil; 1913 in judo sense. Black power is from 1966, associated with Stokely Carmichael.