Having more than the usual number of digits (fingers or toes).
The supernumerary digit may vary from a soft tissue to a complete functioning digit.
Polydactyly (n.) is a congenital abnormality not uncommon in cats; polydactyl cats are known by many names, such as Hemingway cats, mitten cats (cats with mitten feet), thumb cats, Cardi cats, and six-finger cats.
Cf. syndactyl foot