Clinker
Part of speech: noun
Definition: Slag or ash produced by intense heat in a furnace, kiln or boiler that forms a hard residue upon cooling. Hardened volcanic lava. A scum of oxide of iron formed in forging. A very hard brick used for paving customarily made in the Netherlands. A mass of bricks fused together by intense heat. One who clinks or an item that clinks, hence fetters are also called clinkers. Clink, derived from clinch, hence one who clinches or that clinches.
Cinder
Part of speech: noun
Definition: Partially or mostly burnt material that results from incomplete combustion of coal or wood etc.An ember.Slag from a metal furnace.
Part of speech: verb
Definition: to reduce something to cinders