Vellon
A term used in connection with the Spanish coinage to indicate inferior silver, as distinguishable from the plata, or sterling silver. In the reign of Joseph Napoleon as King of Spain (1808-1814), the Duro of twenty Reales is known as the Duro de Vellon, and the Duro of eight Reales as the Duro de Plata.
Source: Frey's Dictionary (American Journal of Numismatics, Vol. 50, 1916)