The term UNFAITHFUL ONE can be broken down into three crossword solutions: RAT (3 letters), TRAITOR (7 letters), and TWOTIMER (8 letters). A RAT is a small rodent that is known for its slyness and cunning. A TRAITOR is someone who betrays their country, friends, or principles. A two-timer is someone who is unfaithful in a relationship by being involved with more than one person at the same time. All three of these terms refer to someone who is not faithful or loyal.