I believe the answer is:
Aristocracy
democrat
monocrat
Aristocracy means a condition when the nobles <em>rule</em> over the people within a society. Democrat means a society that is<em> ruled</em> over by the will of the majority of the people. Monocrat meeans a society that is<em> ruled </em>over by one single person alone.
Since its a sibling, and siblings tend to be in a person's close circle of people, informal speech is used.
