a sudden, violent overthrow of an existing government; (French) literally, blow of state

a coup (coup d'état - literally a "blow of state") is the unconstitutional and forcible replacement of a government by another government without a war or causing a major restructuring of the state. The assassination of a president to form a new presidency, or the military take-over of a state may be extraordinary, but the state and the lives of its citizens may be changed very little. Coups are very difficult in a democracy, and even more difficult in a federation.

a sudden and decisive change of government illegally or by force

Coup d'Etat was a company-wide crossover event published by Wildstorm Comics in 2004. The story ran across 4 issues, each featuring one of the major titles in the Wildstorm Universe at that time: Sleeper, , Wildcats 3.0 and The Authority. It also included an aftermath issue including a preview to the second volume of Sleeper and a preview to the second volume of Wetworks.