E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Coup de Jarnac. A peculiar stroke of the sword by which the opponent is ham-strung. The allusion is to
the duel between Jarnac and La Châteigneraie, on July 10th, 1547, in the presence of Henri II., when Jarnac dealt his adversary such a blow, from which he died.