meg ‧ a ‧ lo ‧ ma ‧ ni ‧ a /ˌmeɡ ə ləʊˈmeɪniə $ -loʊ-/ BrE AmE noun [uncountable]
[ Date: 1800-1900 ; Origin: megalo- 'large' (from Greek megas ; ⇨ ↑ mega- ) + mania ]
when someone wants to have a lot of power for themselves and enjoys having control over other people’s lives, sometimes as part of a mental illness