Which term describes a pathological obsession with one idea or subject?

Monomania specifically refers to an obsessive preoccupation with a single idea or subject to the extent that it significantly impairs a person's ability to function normally in various aspects of life. This term is derived from the roots "mono," meaning one, and "mania," which implies an excessive enthusiasm or obsession.

This condition entails a narrow focus where an individual is unable to think about anything else beyond that particular idea or subject, almost to the exclusion of all else. In contrast, the other terms, while related to obsessional behaviors or thoughts, describe different types or manifestations of mental preoccupations. Obsession can refer more broadly to persistent thoughts that may involve more than one subject. Fixation typically indicates a strong attraction or attachment to an idea or object, but not necessarily to the pathological intensity of monomania. Compulsion usually involves the performance of particular behaviors driven by an impulse rather than a singular, obsessive thought focus. Thus, monomania is the term that most accurately conveys the condition of being pathologically obsessed with one specific idea or subject.