Define electronegativity. How does it differ from electron gain enthalpy?

Electronegativity is defined as the tendency of an element to attract the shared pair of electrons towards itself in a covalent. The is no specific units for electronegativity.It is only a relative tendency.

Electron gain enthalpy is the energy released when one mole of the electron are added to gaseous atoms of an element. It can be negative or positive depending upon whether the electrons is added or removed. An element has a constant value of the electron gain enthalpy that can be measured experimentally.