USURP’, v. t. s. as z. [Fr. usurper ; L. usurpo.] 
    To seize and hold in possession by force or without right; as usurp a throne; to usurp the prerogative of the crown; to usurp power. To usurp the right of a patron, is to oust or dispossess him. 
    Vice sometimes usurps the place of virtue. Denham. 
American Dictionary of the English Language, Noah Webster 1828, Vol. II, page 105.

USURPA’TION, n. [supra.] 
    The act of seizing or occupying and enjoying the property of another, without right; as the usurpation of a throne; the usurpation of supreme power. Usurpation, in a peculiar sense, denotes the absolute ouster and dispossession of the patron of a church, by presenting a clerk to a vacant benefice, who is thereupon admitted and instituted. Cyc. 
American Dictionary of the English Language, Noah Webster 1828, Vol. II, page 105.

USURP’ER, n. 
    One who seizes or occupies the property of another, without right; as the usurper of a throne; of power; or of rights of a patron. Shak. Dryden. Cyc. 
American Dictionary of the English Language, Noah Webster 1828, Vol. II, page 105.

USURPATION. The unlawful assumption of the use of property which belongs to another; an interruption or the disturbing a man in his right and possession. Tomi. 
    There are two kinds of usurpation: first, when a stranger, without right, presents to a church and his clerk is admitted; and, second, when a subject uses a franchise of the king without lawful authority. Co. Litt. 277 b. 
    In Governmental Law. The tyrannical assumption of the government by force, contrary to and in violation of the constitution of the country. 
Bouvier’s Law Dictionary, Third Revision (8^th Edition)(1914), Volume 3, page 3380.

USURPER. One who assumes the right of government by force, contrary to and in violation of the constitution of the country. Toul. Droit. Civ, n. 32. 
    One who intrudes himself into an office which is vacant, and ousts the incumbent without any color of title whatever; his acts are void in every respect; McCraw v. Williams, 33 Gratt. (Va.) 513; Hooper v. Goodwin, 48 Me. 80. 
Bouvier’s Law Dictionary, Third Revision (8^th Edition)(1914), Volume 3, page 3380.

usurpation (ü-zêr-pä’shon). The absolute ouster or dispossession of a patron by a stranger who has no right to do so presented a clerk to a benefice who was thereupon admitted to the living and instituted therein. See. 3 Bl. Comm. 242. 
Law Dictionary, James A. Ballentine, Second Edition, 1948, page 1324.

usurper (ü-zêr-pêr). A person who assumes possession of an office, who performs the duties, and who neither lawful title nor color of right. See Hamlin v. Kassafer, 15 Ore. 456, 3 Am. St. Rep. 176, 179, 15 Pac. Rep. 778. 
Law Dictionary, James A. Ballentine, Second Edition, 1948, page 1324.

USURPATION. The unlawful assumption of the use of property which belongs to another; an interruption or the disturbing a man in his right and possession. Tomlins. 
    The unlawful seizure or assumption of sovereign power; the assumption of the government or supreme power by force or illegally, in derogation of the constitution and of the rights of the lawful ruler. 
    "Usurpation” for which writ of prohibition may be granted involves attempted exercise of power not possessed by inferior office. Ex parte Wilkinson, 220 Ala. 529, 126 So. 102, 104. 
Black’s Law Dictionary 4^th Edition (1951) page 1713.

USURPER. One who assumes the right of government by force, contrary to and in violation of the constitution of the country. Toul. Droit. Civ, n. 32. 
Black’s Law Dictionary 4^th Edition (1951) page 1713.

u|surp (yöö zurp’, -surp’) vt. [[ME usurpen < MFr usurper < L usurpare < usus, a use + rapere, to seize: see rape]] to take or assume (power, a position, property, rights, etc.) and hold in possession by force or without right – vi. to practice or commit usurpation (on or upon) – usurp’er n. – usurp’ing|ly adv. 
Webster’s New World Dictionary, 3^rd College Ed. (1988) page 1470.

u|surpation (yöö zer pä’shen, -ser-) n. [[ME usurpacion < L usuparetio]] the act of usurping; esp., the unlawful or violent seizure of a throne, power, etc. 
Webster’s New World Dictionary, 3^rd College Ed. (1988) page 1470.

Source: http://www.pixi.com/~kingdom/usurp.html