supernumerary
adjective formal uk/ˌsuː.pəˈnjuː.mər.ər.i/ us/ˌsuː.pɚˈnuː.mə.rer.i/
多余的，过剩的，额外的
in addition to the number usually needed
Supernumerary teeth often are found in the upper jaw just behind the front teeth. 多生牙常见于上颌前牙后面。
supernumerary
noun [ C ] formal uk/ˌsuː.pəˈnjuː.mər.ər.i/ us/ˌsuː.pɚˈnuː.mə.rer.i/
冗员，临时雇员;跑龙套的小配角，临时演员
an 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. 他们都是临时雇来的小配角，在歌剧舞台上既不说话也不唱歌，但他们的存在对于演出却是至关重要的。