"But back in the 18th and 19th centuries, it was common to hear shopkeepers talk of "bumper business" in the holiday season or even "bumper traffic" on city streets. "Bumper" as a noun was even used as theatrical slang for a sold-out house at a performance.

The logic of this "large" sense of "bumper" is a little hazy, but a clue may be found in its earliest use. A "bumper" in the 17th century was a large glass of beer or wine that was filled to the brim, i.e., with the liquid literally bumping against the rim of the glass. Such abundance was obviously considered a good thing, as "bumper crops" of just about anything have been ever since.'

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