The ... of the Greeks. At first it designated a small silver coin in the East, but later came to be applied to a copper coin. In the Persian Empire it corresponded to the Greek Obol. It was also popularly applied to Charon's Obol (q.v.) according to Suidas and other ancient authors. The word persisted until the Middle Ages as the Arabic daneq, the Persian dangh and the neo-Sanscrit tanka.
Source: Frey's Dictionary (American Journal of Numismatics, Vol. 50, 1916)