Webster’s Revised Unabridged Dictionary · 1913
Colcothar
Col′co·thar (kŏl′kō·thẽr), n. [NL. colcothar vitrioli, fr. Ar. qolqoṭar.] (Chem.) Polishing rouge; a reddish brown oxide of iron, used in polishing glass, and also as a pigment; — called also crocus Martis.