imperium

imperium [De].
Latin word for a command, which grew to signify the right to give orders, and so to mean supreme power, normally equivalent in the later Roman period to ‘empire’. Imperator, originally ‘commander-in-chief’, became a title used by the emperors, and came to signify ‘emperor’. The Latin writers of the Dark Ages could use imperium of a single kingdom, but the word retained the connotation of a kingdom supreme among others.