A compulsive or irrational preoccupation. / An unhealthy fixation. / Influence or control by evil spirits without possession.

plural of obsession

Prone to cause obsession. / Having one thought or pursuing one activity to the absolute or nearly absolute exclusion of all others. / Excessive, as results from obsession.

A person who is obsessed, who has an obsession.

(passive, constructed with "with") To be preoccupied with a single topic or emotion. / (transitive) To dominate the thoughts of someone.

simple past tense and past participle of obsess

Intensely preoccupied with or by a given topic or emotion; driven by a specified obsession.

present participle of obsess

The characteristic of being obsessive.

In an obsessive manner. / To an obsessive degree.