Words shift, and how they shift matters.
The word "Emperor" today means, "the ruler of an empire": a sovereign with supreme military, political, executive power over many nations.
The origin of the word is "imperātor", a title granted by the Roman Senate - a Republican Institution - to Julius Ceaser, and then his nephew Octavian.
At the time, the title had a strictly military connotation. The imperator was the "person giving orders, commanding officer" in a military, and the purple he wore was a symbol of his military office.
Under Augustus, and throughout the centuries that followed, the meaning shifted to "imperāre": "to demand the production of, levy, give orders, exercise authority, hold political power".
Military power became executive and political.