C1 确切知道；肯定地说
to know or say something without doubt
I don't know for certain if she's coming. 我不能肯定她是否会来。
I can't say for certain how long I'll be there. 我说不准我在那儿会呆多久。
There's very little we know for certain about his emotional life.
She knew for certain that his problems went beyond being in debt.
After a year of investigations, no one can yet say for certain why she was killed.
See also: certain adjective (WITHOUT DOUBT)