Is it farther or further?
late 14c., "having a commanding quality," from Old French imperial (12c.), from Latin imperialis "of the empire or emperor," from imperium (see empire). Meaning "pertaining to an empire" (especially the Roman) is from late 14c. Imperial presidency in a U.S. context traces to Arthur Schlesinger Jr.'s book on the Nixon administration (1974). Related: Imperially.