noun tel??lu??ri??um ??-??lu??r-??-??m, te-\Definition of TELLURIUM : a semimetallic element that occurs in a silvery-white brittle crystalline form of metallic luster, in a dark amorphous form, or combined with metals and that is used especially in alloys and catalysts ??? see element table See tellurium defined for kids Take a 3 minute break!