hydra
n. countablen. a difficult problem that seems to grow or get worse every time you try to fix one part of it.
n. a multifaceted or persistent problem that proves difficult to eradicate because new obstacles appear as soon as one is resolved. Often used as a metaphor for complex political or social issues.
The city's traffic problem is a hydra that resists every solution.
The illegal drug trade is a hydra; as soon as one route is closed, three more appear elsewhere.
The bureaucracy of the tax code has become a hydra, where every attempt at simplification only seems to generate a fresh layer of confusing regulations.
From Latin Hydra, the mythical serpent, originally from Ancient Greek ὕδρα (húdra), from Proto-Indo-European *údreh₂ (“aquatic”). Doublet of otter.
When referring to the mythological creature or the metaphor, it is often capitalised; in biology, it refers to a small freshwater organism and remains lowercase.