Entry 1 sense Webster, 1913 Munchausenism · Mun·chau·sen·ism · IPA /ˈmʊŋk(h)aʊzəˌnɪzəm/ 01 n. An extravagant fiction embodying an account of some marvelous exploit or adventure. 1. An extravagant fiction embodying an account of some marvelous exploit or adventure.