What is a “Compulsion”?

How would you define the word “compulsion”? We sometimes think of it in the positive sense, like in those first stages of a young love when we have a compulsion to spend time with a person or do nice things for them. There is also the negative side to such a powerful word. What about when we feel a compulsion to drink or strike out in anger or even the seemingly more mundane compulsions we hear about like repeated hand washing or clock checking? I looked up a few definitions for “compulsion” and