'Swear' in the Bible

Jonathan made David vow again because of his love for him, for Jonathan loved him as himself.

So now swear to me by the Lord that you will not cut off my descendants after me and that you will not destroy my name from my father’s household (extended family).”

Then David said to him, “Will you take me down to this band [of raiders]?” And he said, “Swear to me by God that you will not kill me or turn me over to the hand of my master, and I will bring you down to this band.”