'Witness' in the Bible

because they have wrought folly in Israel, and have committed adultery with their neighbors wives, and have spoken words in my name falsely, which I commanded them not; and I am he that knoweth, and am witness, saith Jehovah.

Then they said to Jeremiah, Jehovah be a true and faithful witness amongst us, if we do not according to all the word wherewith Jehovah thy God shall send thee to us.