The term 'Decisive Element' can be defined as a DETERMINANT, which is an 11-letter word. It is used to describe something that has a decisive or influential role in a situation. This could be a person, an event, or a factor that affects the outcome of a situation. It is often used to refer to the most important element in a decision-making process. In other words, it is the element that will ultimately determine the outcome of a situation.