Word of the Day:

: an idea that dominates one's mind especially for a prolonged period : obsession

The fear that he was going to be fired became such an idée fixe for Toby that he could think of nothing else.

According to The New Grove Dictionary of Music and Musicians, the term "idée fixe" was coined by French composer Hector Berlioz in 1830, who used it to describe the principal theme of his Symphonie fantastique. That reference goes on to say that, at about the same time, French novelist Honore de Balzac used "idée fixe" in Gobseck to describe an obsessive idea. By 1836, Balzac's more generalized use of the term had carried over into English, where "idée fixe" was embraced as a clinical and literary term for a persistent preoccupation or delusional idea that dominates a person's mind. Nowadays "idée fixe" is also applied to milder and more pedestrian obsessions.