'Witness' in the Bible

because they have worked folly in Israel, and have committed adultery with their neighbors' wives, and have spoken words in my name falsely, which I didn't command them; and I am he who knows, and am witness, says Yahweh.

Then they said to Jeremiah, Yahweh be a true and faithful witness among us, if we don't do according to all the word with which Yahweh your God shall send you to us.