From The Collaborative International Dictionary of English v.0.48:
Clinker \Clink"er\ (kl[i^][ng]k"[~e]r), n. [From clink; cf. D.
clinker a brick which is so hard that it makes a sonorous
sound, from clinken to clink. Cf. Clinkstone.]
1. A mass composed of several bricks run together by the
action of the fire in the kiln.
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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.
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3. A scale of oxide of iron, formed in forging.
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4. A kind of brick. See Dutch clinker, under Dutch.
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