idée fixe

noun2

1. •
   An idea dominating the mind and maintained despite evidence to the contrary; (loosely), an obsession.

   • [“]A foreign policy of domination through spiritual means is [Jorane Sutt’s] idée fixe, but it’s my notion that his ultimate aims aren’t spiritual.[”] — 1951
2. •
   A recurring musical theme; a leitmotif.

   • a definite musical figure, called the 'idée fixe,' unifying the work throughout by its constant reappearance in various aspects and surroundings — 1922