noun

1. slag, as from the reduction of metallic ores
2. a rough piece of solid lava from a volcano
3. any matter, as coal or wood, burned out or partly burned, but not reduced to ashes
4. a minute piece of such matter
5. a coal that is still burning but not flaming
6. ashes from coal or wood

Etymology: ME & OE sinder, dross of iron, slag < IE base *sendhro-, coagulating fluid > Ger sinter, dross of iron, stalactite, sintern, to trickle, coagulate, Czech śadra, gypsum

transitive verb

1. Rare to burn to cinders
2. to cover with cinders