Definitive is a word that signifies an end or conclusion. Some other synonyms for definitive include conclusive, final, ultimate, authoritative, irrefutable, and ultimate. These words are used to describe something that is considered the final word on a matter or subject. When you use a definitive word, it means that there is no doubt or question that what you are saying is the truth. You can use other words like undeniable, determined, and settled to convey a similar meaning. These synonyms can give more weight to your statement and make it sound more convincing and final. When you use words like these, you show that you have researched and understood the topic at hand.