Longman Dictionary of Contemporary English - compulsion

~ n 1 a strong and unreasonable desire that is difficult to control  (Constantly washing her hands became a compulsion that needed treatment. | compulsion to do sth)  (I had a sudden compulsion to hit her.) 2 a force or influence that makes someone do something  (compulsion to do sth)  (Please note that you are under no compulsion to sign the agreement.)  (- see also compel)