Clinker

Part of speech: noun (n.)

1. A mass composed of several bricks run together by the action of the fire in the kiln.

2. Scoria or vitrified incombustible matter, formed in a grate or furnace where anthracite coal in used; vitrified or burnt matter ejected from a volcano; slag.

3. A scale of oxide of iron, formed in forging.

4. A kind of brick. See Dutch klinker, under Dutch.