Entry 1 sense Webster, 1913 Megalomania /mĕgˌ-əl-ōm-ān'-ē-ə/ · Meg·a·lo·ma·ni·a · IPA /ˌmɛɡəloʊˈmeɪniə/ 01 n. A form of mental alienation in which the patient has grandiose delusions. 1. A form of mental alienation in which the patient has grandiose delusions.(Pathol.)