(1):
(n.) The act of usurping, or of seizing and enjoying; an authorized, arbitrary assumption and exercise of power, especially an infringing on the rights of others; specifically, the illegal seizure of sovereign power; - commonly used with of, also used with on or upon; as, the usurpation of a throne; the usurpation of the supreme power.
(2):
(n.) Use; usage; custom.