swear
To take an oath, to promise intensely, solemnly, and/or with legally binding effect.
Example
“The knight swore not to return to the palace until he had found the treasure.”
Other meanings
To take an oath that an assertion is true.
“The witness swore that the person she had seen running out of the bank was a foot shorter than the accused.”
To promise intensely that something is true; to strongly assert.
“I swear I don't know what you're talking about.”
Example sentences
Word history
From Old English "swerian" (to swear, take an oath of office).
Where this comes from
This definition is adapted from “swear” on Wiktionary, by its contributors; example sentences are from Tatoeba, credited to their authors above, published under CC BY-SA 4.0. This page is published under the same licence.