What does "superadd" mean?

Superadd: To add over and above; to add to what has been added; to annex, as something extrinsic. The strength of any living creature, in those external motion, is something distinct from, and superadded unto, its natural gravity. Bp. Wilkins. The peacock laid it extremely to heart that he had not the nightingale's voice superadded to the beauty of his plumes. L'Estrange.