Forswear (which is also sometimes spelled foreswear) is the modern English equivalent of Old English forswerian. It can suggest denial ("[Thou] would'st forswear thy own hand and seal" — John Arbuthnot, John Bull) or perjury ("Is it the interest of any man … to lie, forswear himself, indulge hatred, seek desperate revenge, or do murder?" — Charles Dickens, American Notes). But in current use, it most often has to do with giving something up, as in "The feuding parties agreed to forswear violence" and "She refused to forswear her principles."