/ əbˈseʃn; NAmE / noun obsession (with sth/sb)
1.
[ U ] the state in which a person's mind is completely filled with thoughts of one particular thing or person in a way that is not normal :
Her fear of flying is bordering on obsession.
The media's obsession with the young prince continues.
2.
[ C ] a person or thing that sb thinks about too much :
Fitness has become an obsession with him.
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WORD ORIGIN
early 16th cent. (in the sense siege ): from Latin obsessio(n-) , from the verb obsidere , from ob- opposite + sedere sit.