to use rude or offensive language, usually because you are angry

to make a serious promise to do something

He swore revenge on the man who had killed his father.

I solemnly swear (that) it will never happen again.

I swear (that) I’ll never leave you.

He swore solemnly that he would never hit her again.

She made him swear not to tell anyone.

He left, swearing never to return.

to promise that you are telling the truth

She swore (that) she’d never seen him before.

I could have sworn I heard the phone ring.

I swear to God I had nothing to do with it.

to make a public or official promise, especially in court

Witnesses were required to swear on the Bible.

Are you willing to stand up in court and swear that you don't recognize him?

Remember, you have sworn to tell the truth.

Barons had to swear an oath of allegiance to the king.

I swear by Almighty God to tell the truth.

They refused to swear allegiance to the new ruler.

to make somebody promise not to tell something to anyone

Everyone was sworn to secrecy about what had happened.

LEARNit Dictionary