Coup d'etat

sudden and forcible (usually military) overthrow of a government

A coup d'état (IPA: or AHD: [ko͞o"dā tä]), or simply coup, is the sudden overthrow of a government, often through illegal means by a part of the state establishment — mostly replacing just the high-level figures. It is also an example of political engineering. It can be (although not necessarily) violent, but it is different from a revolution, which is staged by a larger group and radically changes the political system through unconstitutional means.
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Noun
1. a sudden and decisive change of government illegally or by force
(synonym) coup, putsch, takeover
(hypernym) group action
(hyponym) countercoup

n. revolution, coup d'etat, sudden and forcible (usually military) overthrow of a government, overturn, putsch

A quick and decisive extra-legal seizure of governmental power by a relatively small but highly organized group of political or military leaders, typically by means of the unexpected arrest or assassination of the incumbent chief executive and his principal supporters within the government. For the coup to be successful, the rank and file of the police and military have to be willing to take orders from the new government leaders once the coup is accomplished, so typically the organizers of successful coups have previously recruited important military and police commanders to their cause prior to going ahead with it. Most frequently, coups are initiated and led by high-ranking military officers. They are most apt to be successful in countries where both the general population's and the government bureaucracy's ideological dedication to upholding established constitutional procedures is relatively weak and consequently there is little danger of massive civilian resistance or non-cooperation by the rank and file of soldiers and other government employees. [See also: business cycle , recession , Gross Domestic Product , deflation ]