/ ˈmeɪniæk; NAmE / noun
1.
( informal ) a person who behaves in an extremely dangerous, wild, or stupid way
SYN madman :
He was driving like a maniac .
2.
a person who has an extremely strong desire or enthusiasm for sth, to an extent that other people think is not normal
SYN fanatic
3.
( psychology ) a person suffering from mania :
a homicidal maniac
► ma·niac adjective [ only before noun ]:
a maniac driver / fan / killer
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WORD ORIGIN
early 16th cent. (as an adjective): via late Latin from late Greek maniakos , from mania madness , from mainesthai be mad.