Why is the ninth month called September?
c.1300 (early 13c. as a surname), via Anglo-French, from Old French defendeor, agent noun from defendre (see defend). The Latin word in this sense was defensor.
mid-13c., from Old French defendre (12c.) "defend, resist," and directly from Latin defendere "ward off, protect, guard, allege in defense," from de- "from, away" (see de-) + -fendere "to strike, push," from PIE root *gwhen- "to strike, kill" (see bane). In the Mercian hymns, Latin defendet is glossed by Old English gescildeð. Related: Defended; defending.