How does electron affinity differ from electronegativity?

Hint: In one way, electron affinity and electronegativity are essentially the same thing. However they differ slightly in whether they are about attraction or repulsion of electrons. And whether or not they are measurable.

Complete answer:
To put it clearly, the electronegativity of an atom is its ability to attract electrons towards itself. This means that a positively charged ion will attract a negatively charged electron towards itself much more easily than a neutral or negatively charged ion.
Electron affinity on the other hand, deals with the amount of energy required to break an electron away from an ion. The more negative the charge, the harder and harder it is to release an electron from the molecule, and the greater the amount of energy released. Both these properties increase as the atom goes either up or down the periodic table.
As these two properties are in relation to the tendency to attract or repulse electrons, they would be inversely proportional to one another. As electron affinity increases, electronegativity will decrease.

However, the energy required to move an electron away from an atom or molecule is known as ionisation energy. It determines how easily an atom out molecule can give away an electron. However, the loss or sharing of an electron is not the only event. In covalent bonds, the electron is shared with neither party losing or gaining an electron. Instead, the ion with the highest charge will pull the electrons towards itself. The sharing is not equal.

Note: A major difference between the two properties is that electron affinity is a fixed measurable value. Electronegativity however is measured in relation to other atomic properties and will vary depending on the chemical environment.