The crossword solution for the term ONE UNDER OATH is 'SWEARER' which is a 7 letter word. A swearer is someone who makes a solemn promise or commitment to tell the truth, such as in a court of law. This is known as taking an oath and is done by swearing on a holy book or other object of significance. The act of swearing an oath is a way to show respect for the law and to demonstrate one's commitment to telling the truth.