An irresistible urge or bad habit; a strong uncontrollable desire or compulsion to do something harmful or bad.
From Greek 'kakos' (bad) + 'ethos' (habit). This word was adopted into English from Latin medical texts and refers to psychological compulsions or dangerous habits.
There's a famous phrase 'cacothes scribendi' (the itch to write) that medieval monks used to describe the overwhelming urge to write—they'd use this word to explain why they couldn't stop producing manuscripts even when resources were scarce!
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