English▸ noun [mass noun] the state of being obsessed with someone or something:
she cared for him with a devotion bordering on obsession.
▪ [count noun] an idea or thought that continually preoccupies or intrudes on a person's mind:
he was in the grip of an obsession he was powerless to resist.
– ORIGIN early 16th century (in the sense ‘siege’): from Latin obsessio(n-), from the verb obsidere (see obsess).