supernumeraryadjective
/ˌsuː.pəˈnjuː.mər.ər.i//ˌsuː.pɚˈnuː.mə.rer.i/formalin addition to the number usually needed:
Supernumerary teeth often are found in the upper jaw just behind the front teeth.
supernumerarynoun [ C ]
/ˌsuː.pəˈnjuː.mər.ər.i//ˌsuː.pɚˈnuː.mə.rer.i/formalan extra employee, actor, member of a society, etc.:
They're supernumeraries, the people on an opera stage who neither speak nor sing, yet whose presence in the production is crucial.