clinker
Industrial coal/construction residue with real technical definitions
(n) 1. The incombustible residue, fused into an irregular lump, that remains after the combustion of coal. 2. A partially vitrified brick or a mass of bricks fused together. 3. An extremely hard burned brick. 4. Vitrified matter expelled by a volcano. 5. Slang. A sour note in a musical performance: hit a clinker. A mistake; a blunder. Something of inferior quality; a conspicuous failure: a clinker of a show. 6. Chiefly British. Something admirable or first-rate.
Ouch! I just got hit in the head with a clinker!