megalomania

from WordNet (r) 3.0 (2006)

megalomania
    n 1: a psychological state characterized by delusions of
         grandeur

from The Collaborative International Dictionary of English v.0.48

Megalomania \Meg`a*lo*ma"ni*a\, n. [NL., fr. megalo- + mania.]
   (Pathol.)
   A form of mental alienation in which the patient has
   grandiose delusions.
   [1913 Webster] megalomaniacal