1) A congenital anomaly of the hand or foot, marked by the webbing between adjacent fingers or toes. Syndactylies are classified as complete or incomplete by the degree of joining. Syndactylies can also be simple or complex. Simple syndactyly indicates joining of only skin or soft tissue; complex syndactyly marks joining of bony elements.

2) A union of two or more digits that is normal in many birds (as kingfishers) and in some lower mammals (as the kangaroos) and that occurs in humans often as a hereditary disorder marked by the joining or webbing of two or more fingers or toes.