Note to Hamlet, 1.1.46: "usurp'st"

Act 1, Scene 1, line 46.
usurp'st: usurps. To "usurp" is to take the place of another, without any right or justification. The Ghost has usurped both "this time of night" and the "form" of the dead King Hamlet, because the Ghost is a supernatural, timeless being which has come into the time of the natural world and taken the shape of a natural man.

Brian Blessed as the Ghost of King Hamlet