It is a gallicism from the French "defendre."
"Diary of Samuel Pepys, Complete Transcribed From The Shorthand Manuscript In The Pepysian Library Magdalene College Cambridge By The Rev. Mynors Bright"
Samuel Pepys Commentator: Lord Braybrooke
He, because of a favourite Radical godfather; I, because Honore is an inconvenient gallicism.
"Lucretia, Complete"
Edward Bulwer-Lytton
215. "This is not simply a gallicism, but a corruption of the French on; itself a corruption."
"The Grammar of English Grammars"
Goold Brown