pluralis maiestatis
Definition -
(1) Using a plural pronoun to refer to a single person who holds an exalted position - e.g. refering to the King as "they."
(2) Using the Royal We.
Note: The general phenomenon of refering to oneself with the plural pronoun "we" is called nosism

Example -
"We are not amused by the majestic plural." (Queen Victoria)

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