late 14c., deflouren, "deprive (a maiden) of her virginity," also "excerpt the best parts of (a book)," from Old French desflorer (13c., Modern French déflorer) "to deflower (a garden); to take the virginity of" and directly from Late Latin deflorare, from de- (see de-) + flos "flower" (from PIE root *bhel- (3) "to thrive, bloom"). Sense of "despoil of beauty or grace" is from late 15c. The notion is "to strip of flowers," or of the quality or character of a flower, thus "to ravish."
The French Indians are said not to have deflowered any of our young women they captivated. [James Adair, "The Life of an Indian Trader," London, 1775]