Worst describes the lowest quality or most unpleasant option in a group. It is the superlative form of “bad,” meaning nothing else is as bad as this.
“Worst” comes from Old English “wyrst,” the superlative of “yfel” (evil or bad). It has long been used to mark the extreme negative end of a scale.
“Worst” is to “bad” what “best” is to “good”—they are like negative and positive twins. English built them as opposites on purpose, so your brain can flip quickly between the two extremes.
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