Notice also that modern "épée" used to be "espee"

And the e is prothetic. And after a while, the s was no longer pronounced, and it even dropped out of the orthography, but it left its trace in the accent.

Your spay got me to thinking of scalpel: L scalpellus, scalpellum, diminutive of scalper, scalprum 'chisel, knife' (from earlier *scalp-lo-) from scalpere 'to scratch, carve'; cf. Gk skalops 'mole'.