The coup is a trump reducing play, the virtual discard of a trump by the declarer, because he has too many. This sound rather odd.

The only thing that distinguished a grand coup from its humbler brother, the coup, is that in the reducing play it is winners instead of losers that are ruffed.

Let us illustrate a grand coup, where South had to get rid of three superfluous trumps, in order to make his contract of 6

A Q 7
K 3
K Q 4
A Q 9 6 2
J 9 8 2

A 10 8 7 3 2
J 10 5
10 4 3
Q 9 8 6
J 9 5
7 4 3
K 6 5
A J 10 7 5 4 2
K 8

Contract 6

Opening Lead: A

The A followed by the 2. At trick two South ruffs his good diamond. This play would be automatic with a first class player in this situation. Now a heart to the King reveals the position, the declarer has still two trumps too many.

A heart is lead and the 10 finessed. Dummy is re-entered with the Q, and the King of diamonds is lead and ruffed. This is followed by the K, and small to the
Q, now the A is ruffed with the seven of trumps, leaving this position:

A 7

9 6
J 9 8

10 4
Q 9

K 6

Dummy is entered with the A and a good club is played. If East discards, so does South.