monomania

/ˌˈmɑnoʊˌmeɪniə/

Other forms: monomanias

Someone who suffers from monomania is unhealthily preoccupied with something. If your sister talks about nothing but her collection of vintage lunch boxes, you could call it monomania.

It's one thing to be excited about playing Scrabble or preoccupied with local politics, but when any interest gets out of hand, you can call it monomania. The word monomania, from the Greek mono, "one" and mania, "madness," was coined by a French psychiatrist in the early 1800s. One of the most famous literary cases of monomania is that of Captain Ahab, obsessed with his pursuit of Moby Dick.

Definitions of monomania

1. noun

   a mania restricted to one thing or idea
   synonyms: possession

   type of:

   cacoethes, mania, passion

   an irrational but irresistible motive for a belief or action