Worst means the lowest in quality, the most unfavorable, or the least desirable among a group of things. When you say something is the worst, you're saying nothing else is as bad. If you got your worst grade of the year on a spelling test, every other grade you received was better than that one. If someone calls a rainy day at the beach the worst luck, they mean conditions couldn't have been more disappointing.

The word appears in many common expressions. The worst part of a situation is whatever aspect bothers you most. At worst means considering the most negative possible outcome, like saying, “At worst, we'll have to start the project over.” When something goes from bad to worse, the situation is deteriorating, and when it hits the worst, you've reached rock bottom.

Interestingly, worst can also be used as a verb, though less commonly. To worst an opponent means to defeat them completely, like when a chess player worsts their rival in a tournament.

The opposite of worst is best. These words mark the two ends of any scale of quality or desirability.