Dux

Dux (plural: duces) is Latin for leader (from the verb ducere, 'to lead') and later for Duke and its variant forms (Doge, Duce, etc.).

During the Roman Republic, dux could refer to anyone who commanded troops, including foreign leaders, but was not a formal military rank. In writing his commentaries on the Gallic Wars, Julius Caesar uses the term only for Celtic generals, with one exception for a Roman commander who held no official rank.