black diamond 
noun
1 informal A lump of coal.When first black diamond lumps were found beneath the ancient Appalachian ground a scene that none expected to see became as common as common can be....
- The first black diamonds were mined on ‘Coal Hill,’ now Mt. Washington in Pittsburgh, in the late 1700s.
2A dark, opaque form of diamond. Also called carbonado.‘He got her a black diamond with two gray diamonds on the side,’ says the source....
- Beautiful silver earrings hang from the points of her ears, encrusted by black diamonds and deep purple amethysts.
- Her black dress, shining from some silver silk material with black diamonds sewn into the hems and lines, contrasted with her washed-pale skin.
3 [usually as modifier] North American A difficult ski slope: a steep, black-diamond run...
- While I worry about getting on and off the chairlifts, however, my boyfriend, an experienced snowboarder, starts fantasising about soft, powdery snow, half-pipes and double black diamonds.
- Most Vermont resorts are best suited to intermediate skiers, although with 23 lifts and 145 runs - three of which are double black diamonds - there is more than enough variety to keep any skier busy for a week.
- You look at those tempting black diamonds, so colourfully named (Dog Face, Cascade, Paint Brush) and think, hey, they don't look so difficult.
- walkie-talkie
- walk-in
- walking-around money
- walking bass
- walking beam
- walking beat
- walking boss
- walking bus
- walking cast
- walking catfish
- walking chair
- walking day
- walking delegate
- walking dictionary
- walking disease
- walking doll
- walking dragline
- walking encyclopedia
- walking epidural
- walking fern
- walking fish
- walking frame
- walking funeral
- walking gentleman
- walking leaf