bulletproof I. \ˈ ̷ ̷ ̷ ̷| ̷ ̷\adjective 1.: impenetrable to bullets < bulletproof glass > 2.: not subject to correction, alteration, or modification < a bulletproof argument > II. transitive verb (-ed/-ing/-s) Etymology:bulletproof (I) : to make impenetrable to bullets < bulletproof a car >