All 4 Uses

coup
in
Love in the Time of Cholera
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Yet on two of these occasions someone realized that he and his presumptive male companion did not go to the bar but to a room, and the already tarnished reputation of Florentino Ariza received the coup de grace.†
Chpt 4
"Well, it must be a very special form of cholera," he said, "because every single corpse has received the coup de grace through the back of the neck."†
Chpt 5 *
She knew it was, because she had seen the white lumps in the mouths of the sweltering corpses, but she noted that none of them had the coup de grace in the back of the neck as they had at the time of the balloon.†
Chpt 5
In order to add even greater poignancy to their memories, she had brought her copy of the portrait of them dressed as old-fashioned ladies, taken by the Belgian photographer on the afternoon that a young Juvenal Urbino had delivered the coup de grace to a willful Fermina Daza.†
Chpt 6

Definitions:

(1) (coup as in: deposed in the coup)
the sudden overthrow of a government by use of limited force

This sense of coup is also called a coup d'état.
(2) (coup as in: a financial coup)
a brilliant and notable success

The term "coup de theatre" indicates a sensational moment in a theatrical stagecraft -- typically a surprise; or possibly a highly successful theatrical production.
(3) (coup de grace as in: delivered the coup de grace)
deathblow

(literally a sword strike that mercifully kills a wounded animal, or metaphorically as the last in a series of things that defeated an opponent, idea, business or other entity.)

The term coup de grace indicates a merciful death blow.
(4) (meaning too rare to warrant focus)