0 to use words that are rude or offensive as a way of emphasizing what you mean or as a way of insulting someone or something: --
1 to promise or say firmly that you are telling the truth or that you will do something or behave in a particular way: --
I think his birthday is on the 5th, but I wouldn't/couldn't swear to it (= I am not completely certain about it).
A few of us knew what was going to happen, but we were sworn to secrecy (= we were made to promise to keep it a secret).
I swore an oath to tell the truth, the whole truth, and nothing but the truth.
In some countries, witnesses in court have to swear on the Bible.
[ + to infinitive ] New gang members must swear to obey the gang leaders at all times.
UK informal She swore blind (= promised definitely) (that) she didn't know what had happened to the money.
[ + (that) ] You might find it difficult to believe, but I swear (that) the guy just came up to me and gave me the money.
I want you to swear that you will never try to see her again.
Soldiers must swear allegiance to the Crown.
He swore he'd pay her back for all she'd done to him.
We could hear him cursing and swearing as he tried to get the door open.