(passive, constructed with "with") To be preoccupied with a single topic or emotion.
Some people are obsessed with sports.
To dominate the thoughts of someone.
Thoughts of her obsess my every waking moment.
(construed with over) To think or talk obsessively about.
Stop obsessing over it, will you!
Intensely preoccupied with or by a given topic or emotion; driven by a specified obsession.
Influenced or controlled by evil spirits, but less than possessed in that the spirits do not actually reside in the victim.