Some priests have to forswear marriage.

有些祭司必须宣誓放弃婚姻。

You must tell the truth to the judge, because if you forswear yourself you could go to prison.

你必须向法官说老话，因为你如果伪证就可能坐牢。

The old man forswore smoking.

那老人下决心戒烟。