Clinker

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 clinker, under Dutch.