the domination of one's thoughts or feelings by a persistent idea, image, desire, etc.

the idea, image, desire, feeling, etc., itself.

the state of being obsessed.

the act of obsessing.

noun

indifference

noun

attraction , ax to grind * , bug in ear , case * , complex , compulsion , concrete idea , craze * , crush , delusion , enthusiasm , fancy , fascination , fetish , hang-up * , ide fixe , infatuation , mania , monkey * , must , neurosis , one-track mind * , passion , phantom , phobia , preoccupation , something on the brain , thing * , tiger by the tail , fixation , craving , craze , impulse , incubus