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Prof. Thomas Childers, of the University of Pennsylvania, indicates that the English language’s lacking a word denoting the sudden, violent change of government derives from England’s stable political traditions and institutions. Although French and German history are coloured with such politico-military actions, English history is not.

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You must be thinking of Crème Pâtissière ;)

It"s from the french, coup meaning an unexpected strike or blow and d'etat meaning the state. Thus an unexpected strike against the state. It sounds nicer in french.