Dominion is defined as control or power over, or the authority to rule.(noun)
When a king has power over a certain territory, this is an example of a situation where a king has dominion over that territory.
See dominion in Webster's New World College Dictionary
Origin: ME dominioun < ML dominio < L dominus: see dominate
See dominion in American Heritage Dictionary 4
Origin: Middle English dominioun
Origin: , from Old French dominion
Origin: , from Medieval Latin dominiō, dominiōn-
Origin: , from Latin dominium, property
Origin: , from dominus, lord; see dem- in Indo-European roots.
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