A somewhat literary or technical term for an obsessive fixation on a single idea or subject. Can refer to the condition or a person with it.
彼は偏狂的なまでに切手収集に没頭している。
He is obsessed with stamp collecting to the point of monomania.
The inventor devoted himself to a single line of research to the extent that he was called a monomaniac.
Sino-Japanese compound of 偏 (へん, 'biased, leaning') and 狂 (きょう, 'madness, insanity'), literally 'biased madness'. The exact historical derivation is uncertain, but it likely entered Japanese as a translation of the Western psychological term 'monomania'.