the.com/bumper

means A protective bar fitted to the front and back of a vehicle to absorb minor impacts in collisions.

from Traces to the verb 'bump,' and first showed up describing cushioning devices that absorb shock — padded buffers on things like train cars and carriage parts — before settling onto automobiles. The 'bumper' as brimful drink or bumper crop is a separate, older sense from the 1600s-1700s, likely tied to a 'bumping' glass filled to the brim; the automotive bumper is the later, unrelated descendant of plain old 'bump.'