Definitively means in a way that settles something completely and finally, leaving no room for doubt or further debate. When scientists definitively prove that a medicine works, they've gathered so much solid evidence that there's no reasonable question left about it. When a referee definitively calls a runner out at home plate, they've seen it clearly and made a final decision that won't be reversed.

Think of the difference between a teacher saying “I think this answer is right” versus “This is definitively the correct answer.” The second statement closes the discussion.

People often use this word when describing conclusions backed by overwhelming evidence or when someone in authority makes a binding decision. A judge might definitively rule on a case. A DNA test might definitively identify someone. An archaeological discovery might definitively prove where an ancient civilization lived.

Be careful not to confuse definitively with definitely. “Definitely” just means “certainly” or “for sure” (like “I'm definitely going to the party”). “Definitively” means something has been settled in a final, conclusive way. You can be definitely sure about something in your own mind, but something is only resolved definitively when the question is answered completely for everyone.