1911 Encyclopædia Britannica/Clinker

CLINKER. (1) (From an old Dutch word klinkaerd, from klinken, to ring), a hard paving brick, a brick with a vitrified surface, or a fused mass of brick; also the incombustible residue of coal, which occurs, half-fused into hard masses, in grates or furnaces; a fused mass of lava. (2) (From clinch, or clench, a common Teutonic word, meaning “to fasten together”), a term appearing usually in the form “clinker-built” as opposed to “carvel-built,” for a boat whose strakes overlap and are not fastened “flush.”