A bumper is a bar or shield on the front or back of a vehicle that helps protect it in minor collisions. Informally, “bumper” can also mean unusually large, as in a bumper crop.
The vehicle part comes from “bump,” meaning “to hit,” plus “-er,” a thing that does something. The “large amount” sense may come from 18th-century drinking, where a “bumper” was a full glass.
A car’s bumper is literally the part that takes the bumps for you. The “bumper year” sense grew from the idea of a cup filled right to the brim—nature’s version of an overflowing drink.
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