'Witness' in the Bible

Because that they have done folly in Israel, and commit adultery with the wives of their neighbours, and speak a word in My name falsely that I have not commanded them, and I am He who knoweth and a witness -- an affirmation of Jehovah.

And they have said to Jeremiah, 'Jehovah is against us for a witness true and faithful, if -- according to all the word with which Jehovah thy God doth send thee unto us -- we do not so.