From Longman Dictionary of Contemporary Englishmonomaniamon‧o‧ma‧ni‧a /ˌmɒnəʊˈmeɪniə $ ˌmɑːnoʊ-/ noun [uncountable] formal OBSESSIONa very strong interest in one particular idea or subject which prevents you from thinking about anything else an obsession with food that verged on monomania —monomaniac /-niæk/ noun [countable]
Examples from the Corpus
monomania• She has an obsession with the drug that verges on monomania.• Such monomania has been useful to warriors since long before the silicon age.• Thus, finally, Ahab recognizes the monomania of his pursuit, but can do nothing about it.• Can I explain to her that I am fully in sympathy with their monomania? 