The crossword solution for the term 'Worthless Old Coin' is SOU. This is an abbreviation for the Latin term 'solidus', which was a gold coin used in the Roman Empire from the 4th century until the 11th century. The solidus was also used in the Byzantine Empire and was one of the most important coins of the Middle Ages. In modern times, the term 'sou' is used to refer to any old or worthless coin.