To swear means to make a solemn promise or to use offensive language.

When you swear to tell the truth in court, you're making the most serious kind of promise, one that carries legal consequences if you break it. The President swears an oath when taking office, promising to uphold the Constitution. When someone says “I swear I didn't eat the last cookie,” they're emphasizing that they're telling the truth.

But swear also means using words considered rude, offensive, or vulgar. These swear words (also called profanity or curse words) are expressions that many people consider inappropriate, especially in formal settings or around certain people. Different families and communities have different standards about which words count as swearing and how serious it is. Someone might swear in anger when they stub their toe or drop something heavy.

The two meanings connect through the idea of powerful language. A sworn promise uses words at their most serious and binding. Swear words are considered powerful too, but in a negative way: they're words meant to shock or express strong emotion. That's why both are treated as special kinds of speech with real consequences.