Debasement is the process of spoiling something or reducing its value by combining it with another material. Debasement can also refer to degrading or disgracing someone.
The noun debasement can be used in an economic context to mean "lower the value of currency or money," usually referring to coins made of gold or silver that has been mixed with cheaper metals. In the old days, debasement generally meant the removal of someone's knighthood: "The knight's treasonous actions meant certain debasement by the king." Today you might hear someone complain about the debasement of politics caused by big money.