megalomania

noun3

1. •
   A psychopathological condition characterized by delusional fantasies of wealth, power, or omnipotence.

   • As to Ernest... He is quite as nervously broken down as I am but it manifests itself in different ways. His inclination is towards megalomania and mine towards melancholy. — 1936
2. •
   An obsession with grandiose or extravagant things or actions.
3. •
   (no longer used) Narcissistic personality disorder.