obsession

Compulsive preoccupation with a fixed idea or an unwanted feeling or emotion, often accompanied by symptoms of anxiety.

A compulsive, often unreasonable idea or emotion.

In pathology, a constant brooding upon any subject, such as the thought of death, until the mind becomes dominated by that one idea.

The act of besieging; persistent assault.

Continuous or persevering effort supposed to be made by an evil spirit to obtain mastery of a person; the state or condition of a person so vexed or beset: distinguished from possession, or control by a demon from within.

The act of besieging.

The state of being besieged; — used specifically of a person beset by a spirit from without.

An excessive preoccupation of the thoughts or feelings; the persistent haunting or domination of the mind by a particular desire, idea, or image.

Any driving motive; a compelling goal; — not necessarily implying a negative judgment, as does sense 3

Something that causes an obsession{3}.