a many-headed creature (from Greek mythology), or something that seems impossible to defeat because new problems arise when old ones are solved.
From Latin and Greek 'hydra,' literally meaning water-snake ('hydro-' water + root meaning snake). In mythology, the Hydra had multiple heads that regrew when cut off. The term evolved to describe any persistent, multiply-sourced problem.
The mythological Hydra was undefeatable because cutting off one head caused two to grow back—which is why we still use 'hydra' to describe problems like corruption or social issues that seem to multiply the more you fight them!
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