A person who has an excessive desire for power or who believes they are much more important and powerful than they actually are.
From Greek 'megalos' (great) + 'mania' (madness, obsession) + '-ac' (one affected by). The term emerged in the late 1800s in psychology to describe a mental disorder.
The same 'megalo-' prefix appears in 'megalodon' (giant prehistoric shark) and 'megalith' (huge stone)—but with a megalomaniac, it's about their inflated perception of their own greatness!
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