Learner's definition of OBSESSION
a state in which someone thinks about someone or something constantly or frequently especially in a way that is not normal
He was fascinated by the actress and tracking her every move had become an obsession.
She has an obsession about cleanliness.
the object of her obsession [=the thing that she is obsessed about]
The restaurant's menu is evidence of the chef's lifelong obsession with international cuisines. [=the chef's lifelong interest in international cuisines]
someone or something that a person thinks about constantly or frequently
an activity that someone is very interested in or spends a lot of time doing
[more obsessional; most obsessional]