Definition of Supernumerary

Supernumerary: Beyond the normal number. Anything supernumerary is extra.

A supernumerary chromosome is an extra one beyond the usual number of 46. A supernumerary digit is an extra finger or toe. A supernumerary nipple is an extra nipple beyond the usual one on either side. A supernumerary placenta is an extra placenta (afterbirth) and is called an accessory or succenturiate placenta.