idée fixe.

An idea or conviction that holds a person's attention so firmly that it resists contrary considerations.

Use it for

Words that belong together

• a governing idée fixe
• become an idée fixe
• someone's idée fixe

On the page

The locked room became his idée fixe, eclipsing even the disappearance that had brought him there.

Her idée fixe was not that he would return, but that he had never truly left.

Usage notes

Primary category: horror. Forms: Singular idée fixe; plural idées fixes. Legacy lexical fields mirror sense 1 only. Use numbered sense fields for all meanings.