I think the element that has been correctly defined by Antoine Lavoisier would be the element oxygen. He is famous for the discovery of the importance of the molecule oxygen in the process of combustion. He is is the one who characterized and named the element oxygen and hydrogen. Also, showing how these atoms combine in order to form a water molecule in the combustion process. He is considered as the father of modern chemistry as he helped in organizing nomenclature of the chemical compounds. He also is responsible for laying the foundations of the famous law of conservation of mass.