If you see a word you do not know then you look in the Oxford English Dictionary. Here you go!!
In Psychol.: delusions of power or self-importance, esp. resulting from mental illness; a passion for grandiose schemes. More generally: lust for power, a desire to control.
1887 Polit. Sci. Q. 2 157 Dr. François Roy of Quebec testified..that [Louis] Riel was..afflicted with a form of insanity known as megalomania, by which he labored under a delusion that he had a mission to perform for the Métis. 1890 J. S. BILLINGS National Med. Dict. II. 723 Monomania involving the idea of a divine or celestial origin or connection..[is] a species of megalomania. 1892 Contemp. Rev. Feb. 166 Here again megalomaniathe desire to ‘do the great’had the upper hand. 1897 LD. SALISBURY in Daily Chron. 17 Nov. 8/2 A common intellectual complaint..which I may name (as I see Mr. Gladstone has consecrated the word) megalomaniathe passion for big things simply because they are big. 1904 A. GRIFFITHS Fifty Years Public Service xiv. 222 Megalomania was strangely prevalent among these criminal lunatics. 1914 W. J. LOCKE Jaffery viii, This is absurd. It's megalomaniala folie des grandeurs. 1959 Listener 17 Sept. 451/3 The later rake's progress toward corruption, aggression, humiliating subjection to Hitler, pathological megalomania and final catastrophe. 1974 F. FORSYTH Dogs of War II. ix. 169 Megalomania..is present in many people outside lunatic asylums and is usually..interpreted, at least when present in the rich and famous, as merely exaggerated egocentricity. 1993 Toronto Sun 17 June 12/1 The Tories reveal their megalomania, insecurity and arrogant intolerance for dissent.
Now I want to see if you are paying attention to everything I write...pardon my grammar. What am I reading?