plumbago (n.)
"graphite," 1784, from Latin plumbago "a type of lead ore, black lead," from plumbum "lead" (see plumb (n.)); it renders Greek molybdaina, which was used of yellow lead oxide and also of a type of plant (leadwort). Attested in English in the yellow oxide sense from 1610s; as a type of plant from 1747. Related: Plumbaginous.