The term 'Iranian of Old' refers to the ancient Persian Empire, which was ruled by the Achaemenid dynasty from 550 BCE to 330 BCE. The crossword solution for this term is MEDE, which is an alternative spelling of the ancient Persian tribe known as the Medes. The Medes were one of the most powerful and influential tribes in the region during the Achaemenid period, and they played a major role in the formation of the Persian Empire.