In a manner that is foolish, silly, or stupidly self-confident without basis in reality.
From 'fatuous' (adjective meaning foolish) plus the adverb-forming suffix '-ly', describing how an action or statement occurs foolishly.
When someone speaks 'fatuously,' they're saying something ridiculous with complete confidence—this word perfectly captures that cringe-inducing moment when someone obviously intelligent says something obviously stupid.
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