American Heritage Dictionary
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Century Dictionary
(4)
GNU Webster's 1913
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WordNet
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Elsewhere on the web
My honorable friend from Illinois, as it seemed to me--his nature is impulsive, and perhaps he was carried further than he intended--seemed to intimate that the President of the United States had not acted sincerely in this matter; that his usurpation was a clear one, and that he was to be censured for that usurpation.— History of the Thirty-Ninth Congress of the United States
Yet his usurpation is apparently sustained by public sentiment, and a deep wound is inflicted on the constitution, which will be long in healing The danger in this respect is all the greater because it did not originate with the rebellion, but had manifested itself for a long time before.— The American Republic : constitution, tendencies and destiny
Vitalis, p 816 The acquisition of Normandy was a great point of Henry's ambition; being the ancient patrimony of his family, and the only territory winch, while in his possession, gave him any weight or consideration on the continent: but the injustice of his usurpation was the source of great inquietude, involved him in frequent wars, and obliged him to impose on his English subjects those many heavy and arbitrary taxes, of which all the historians of that age unanimously complain.— The History of England in Three Volumes, Vol.I., Part A. From the Britons of Early Times to King John
For this purpose they chose from among the most daring of the Janissaries those officers who had a grudge against Halil for enforcing discipline against them, and were also jealous of what they called his usurpation of authority.— Halil the Pedlar A Tale of Old Stambul
The powers concerned have been told by some perfidious Poles, and perhaps they believe, that their usurpation is a great benefit to the people, especially to the common people.— The Works of the Right Honourable Edmund Burke, Vol. 04 (of 12)

Century Dictionary (1)
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You can expect to see this word about twice a month.