Emperor
Middle English (especially representing the title given to the head of the Roman Empire): from Old French emperere, from Latin imperator ‘military commander’, from imperare ‘to command’, from in- ‘towards’ + parare ‘prepare, contrive’.
wiktionary
From Middle English emperour, borrowed from Anglo-Norman emperour and Old French empereor (Modern French empereur), from Latin imperātor(“emperor; commander”), from imperāre(“to command”). Doublet of imperator.
etymonline
emperor (n.)
early 13c., from Old French empereor "emperor, leader, ruler" (11c.; accusative; nominative emperere; Modern French empereur), from Latin imperatorem (nominative imperator) "commander, emperor," from past participle stem of imperare "to command" (see empire).
Originally a title conferred by vote of the Roman army on a successful general, later by the Senate on Julius and Augustus Caesar and adopted by their successors except Tiberius and Claudius. In the Middle Ages, applied to rulers of China, Japan, etc.; non-historical European application in English had been only to the Holy Roman Emperors (who in German documents are called kaiser), from late 13c., until in 1804 Napoleon took the title "Emperor of the French."
