1. A reference to or characterized by an uncontrollable feeling or passion about something or someone: An obsessive concern may cause some people to do things against their wills because they have no ability to stop themselves.
2. Relating to, characteristic of, or causing a desire to do something: Shirley had an obsessive-gambling habit, on and off the internet.
3. An extreme degree or nature: The coach had an obsessive need and desire for his team to win every game they played.

A continuous focus on or brooding about memories, plans, or ideas; some of which are usually not serving any useful purpose: Janet was having obsessive ruminations for weeks before going on the reporting assignment the editor gave her regarding how well the U.S. military families were living in Germany because she had never been to a foreign country before.

In medicine, a neurosis in which people are continuously bothered by persistent ideas that make them do repetitive, ritualized actions which they have no control over: An obsessive-compulsive disorder often begins in adolescence and continues to fluctuate or come and go over time.

People with obsessive-compulsive disorders often suffer from very strong feelings of having to do something that can't be controlled by themselves and so they also may have depressions and anxieties.

For a long time, obsessive-compulsive disorders have been treated with psychoanalysis or behavior therapy.