ETYM Latin obsessio: cf.French obsession.
Persistently intruding thought, emotion, or impulse, often recognized by the sufferer as irrational, but nevertheless causing distress. It may be a brooding on destiny or death, or chronic doubts interfering with everyday life (such as fearing the gas is not turned off and repeatedly checking), or an impulse leading to repetitive action, such as continually washing one's hands.
In obsessive-compulsive neurosis, these intrusions compel the patient to perform rituals or ceremonies, albeit reluctantly, no matter how absurd or distasteful they may seem.
An unhealthy preoccupation with something or someone; SYN. fixation.