To make a solemn promise; to use curse words or profanity; or to assert something as true with strong conviction.
From Old English 'swerian,' related to Old Norse 'sverja,' likely connected to Proto-Germanic roots. Originally meant only 'to make a binding oath,' but later developed to include profanity around the 15th century.
Curse words and oaths come from the same root because swearing an oath meant calling curses on yourself if you lied—you were literally invoking divine punishment. That's why our most intense curse words are so taboo; they started as genuinely dangerous things to say.
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