monarchy

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Government by a monarch.
• noun A state ruled or headed by a monarch.

from The Century Dictionary.

• noun Supreme power wielded by a single person; absolute personal authority.
• noun The principle of government by a monarch; the monarchical system.
• noun A government in which the supreme power is either actually or nominally lodged in the hands of a monarch or sole ruler, who holds his position for life, generally with hereditary succession.
• noun The territory ruled over by a monarch; a kingdom; an empire.
• noun In theology, the doctrine that there is in the Godhead only one principle (ἀρχή), cause (αἰτία), source or fountain (πηγή) of deity, namely God the Father, from whom the Son and the Holy Ghost derive their divinity. Also monorchia.

from the GNU version of the Collaborative International Dictionary of English.

• noun A state or government in which the supreme power is lodged in the hands of a monarch.
• noun A system of government in which the chief ruler is a monarch.
• noun The territory ruled over by a monarch; a kingdom.
• noun a universal monarchy, supposed to be the subject of prophecy in Daniel ii.; the four preceding monarchies being Assyrian, Persian, Grecian, and Roman. See Fifth Monarchy men, under Fifth.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A government with a hereditary head of state (whether as a figurehead or as a powerful ruler).

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an autocracy governed by a monarch who usually inherits the authority