'Certainty' in the Bible

For on the day you leave and cross over the Brook Kidron, know for certain that you shall surely die; your blood shall be on your own head.”

So the king sent word and called for Shimei and said to him, “Did I not make you swear by the Lord and solemnly warn you, saying, ‘Know for certain that on the day you leave [Jerusalem] and go anywhere, you shall surely die’? And you said to me, ‘The word (ruling) I have heard is good.’