define conclusive
If you've got a theory that you're trying to prove, and you uncover a conclusive piece of evidence, then the case is closed. Conclusive means you've got your answer, you've proved your theory, and there can't be any doubt about it. If want to prove that frogs can speak, and you record a frog reciting The Midnight Ride of Paul Revere, that would be conclusive evidence for your claim. But if the frog mumbled and might have been just making frog noises, critics would say that your video is not conclusive.