thinking too much about one particular person or thing, in a way that is not normal He's becoming more and more obsessive about punctuality. an obsessive attention to detailExtra examples She continued on with an almost obsessive determination. She started to get obsessive about tidiness. An obsessive fan was making the singer’s life a misery. He’s becoming more and more obsessive about punctuality. His interest in buildings was obsessive. Most sufferers from obsessive-compulsive disorder are aware that their behaviour is not rational. Some collectors become obsessive. The play is about obsessive jealousy. You need to be obsessive about detail.