1.NounAny element in the d block of the periodic table (i.e. groups 3 to 12 inclusive).
2.NounThe same, but excluding the group 12 elements (i.e. groups 3 to 11 inclusive).
3.NounAny of the group of metallic elements that have an incomplete inner (d) electron shell, having multiple valencies and forming coloured compounds and stable complex ions.