Monomania

имя существительное [медицина] мономания

Большой англо-русский словарь

Monomania

noun Etymology: New Latin 1. mental illness especially when limited in expression to one idea or area of thought 2. excessive concentration on a single object or idea • monomaniac noun or adjectivemonomaniacal adjectivemonomaniacally adverb

Merriam-Webster's Collegiate Dictionary