The seven SI units are: kilogram, meter, second, kelvin,mole, ampere and candela.
Out of these seven, the one that will probably be part of the definition of a lumen is candela.
The luminous intensity of a light source is the the luminous flux emitted by that light source in a unit solid angle. The SI unit of luminous flux is lumen and the SI unit of luminous intensity is lumen divided by steradian [lumen/steradian] which is called Candela.
