emperor [ME] The root of emperor is the Latin word imperare ‘to command’, which is also the ultimate source of empire [ME], imperative [LME], imperial [LME], and imperious [E16th]. Latin imperator meant ‘military commander’, which was given as a title to Julius Caesar and to Augustus, the first Roman emperor, and was adopted by subsequent rulers of the empire. In English, emperor first referred to these Roman rulers, and then to the head of the Holy Roman Empire. See also evil.