cinder

Concise Oxford English Dictionary © 2008 Oxford University Press:
cinder/ˈsɪndə(r)/

▶noun a piece of burnt coal or wood that has stopped giving off flames but still has combustible matter in it.

– derivatives
cindery adjective.

– origin OE sinder ‘slag’, of Gmc origin (cf. sinter); influenced by Fr. cendre (from L. cinis ‘ashes’).