meg·a·lo·ma·ni·a /ˌmeɡ(ə)lōˈmānēə/ noun noun: megalomania obsession with the exercise of power, especially in the domination of others. Similar: delusions of grandeur obsessionalism grandiosity grandioseness self-importance egotism conceit conceitedness folie de grandeur Opposite: modesty humility the delusional belief that one is important, powerful, or famous, as a form or symptom of mental disorder.