Early 19th century; earliest use found in Philosophical Transactions of the Royal Society of London. From French pléonaste from Hellenistic Greek πλεοναστός abundant from ancient Greek πλεονάζειν to be superfluous or redundant, to abound + -τός, suffix forming verbal adjectives; so called from the multitude of faces of the crystal, each solid angle of the octahedron being often replaced by four faces.