bumper noun definition in Parts of a car topic from the Oxford Advanced Learner's Dictionary

bumper

 noun: Parts of a car topic
a bar fixed to the front and back of a car, etc. to reduce the effect if it hits anything a bumper sticker (= a sign that people stick on the bumper of their cars with a message on it) The cars were bumper to bumper on the road to the coast (= so close that their bumpers were nearly touching). The cars crawled along bumper to bumper.