obsession
n. C / Un. a strong interest in something or someone that stops you from thinking about anything else. You use this when a person cares about a topic or hobby way too much.
n. a persistent and inescapable preoccupation with an idea, feeling, or person. Frequently carries a negative connotation of unhealthy fixation or psychological compulsion.
His obsession with video games is starting to ruin his grades.
The detective's obsession with the unsolved case led her to spend every weekend reviewing old evidence files.
What began as a mild interest in historical architecture soon blossomed into a full-blown obsession, prompting him to travel across Europe documenting forgotten ruins.
From Latin obsessio (“a besieging”), from obsidere (“to besiege”); see obsess. Equivalent to obsess + -ion.
Frequently paired with the preposition 'with' to indicate the target of the fixation.