From Longman Dictionary of Contemporary Englishhydrahy‧dra /ˈhaɪdrə/ noun 1 → Hydra2 [countable] formalBAD BEHAVIOUR OR ACTIONS a problem that is very difficult to get rid of because it keeps returning
Examples from the Corpus
hydra• But the regenerative powers of the corporate hydra were insidious.• He drew the sliver of light across that limb of the hydra as if slicing cheese.• Quite quickly the whole corridor filled to the brim with the substance of the hydra.HydraHydraRMa snake in ancient Greek stories with many heads that grow again when they are cut off → hydra 