ruler

noun

person who reigns over a certain region or country
instrument used in geometry, technical drawing, printing, engineering and building to measure distances or to rule straight lines; straightedge which may also contain calibrated lines to measure distances

Pronunciation: /ˈɹuːlə/ / /ˈɹuː.lə/ / [ɹʉwlə]

Etymology: From Middle English reuler; equivalent to rule + -er.

A (usually rigid), flat, rectangular measuring or drawing device with graduations in units of measurement; a straightedge with markings.
“Take this ruler. […] I want you to measure the glass of the lamp.”
A person who rules or governs; someone or something that exercises dominion or controlling power over others.
“The carcharhinids are unquestionably the rulers of the seas, because of their abundance, their strength and speed, and their unchallenged position as the number one predators in the marine ecosystem.”
“LIKE THE MANDARINS of old, the rulers of China live behind high walls. When they emerge, which they rarely do, they travel in cars with rear windows curtained like sedan chairs. They live in the Chung Nan Hai, a walled park adjacent to the Forbidden City from where ancient dynasties ruled the Celestial Empire.”

Etymology: From Middle English reuler; equivalent to rule + -er.