C14: from Old French aseürer to assure, from Medieval Latin assēcūrāre to secure or make sure, from sēcūrussecure
Word Origin and History for assure
v.
late 14c., from Old French asseurer (12c., Modern French assurer) "to reassure, calm, protect, to render sure," from Vulgar Latin *assecurar, from Latin ad- "to" (see ad-) + securus "safe, secure" (see secure (adj.)). Related: Assured; assuring.