# hydra

/ˈhaɪdɹə/ (US) · /hˈaɪdɹɐ/ (UK)

Source: https://englishreference.com/word/hydra
Updated: 2026-08-27

## Senses

### 1. mythology

noun · CEFR C1 · Literary

a monster from Greek stories with many heads that grow back if they are cut off.

For teachers: a multi-headed serpent in Greek mythology, specifically the Lernaean Hydra, which regrew two heads for every one severed.

- In the old stories, Hercules had to fight the Hydra as one of his difficult tasks.
- The myth of the Hydra serves as a classic archetype for an adversary that becomes more formidable with every attempt to destroy it.

### 2. a persistent problem

noun · CEFR C2 · Academic · Formal

a difficult situation or problem that is hard to solve because it keeps growing or changing.

For teachers: a multifarious or persistent problem that is difficult to eradicate because new obstacles appear as soon as old ones are resolved.

- The drug trade is a hydra; as soon as one route is closed, three more open up.
- The bureaucracy had become a hydra, where every attempt at simplification only seemed to generate a fresh layer of complex regulations.

### 3. biology

noun · CEFR C2 · Technical

a tiny animal that lives in fresh water and has long tentacles around its mouth.

For teachers: any of several small freshwater polyps of the genus Hydra, characterized by a cylindrical body and tentacles used for capturing prey.

- The students used microscopes to watch the hydra move its tentacles in the pond water.
- Biologists study the hydra for its remarkable regenerative abilities, as it does not appear to age or die of natural causes.

### 4. astronomy

noun · CEFR C2 · Technical

a large group of stars in the night sky that looks like a long snake.

For teachers: the largest of the 88 modern constellations, representing a water snake and located in the southern celestial hemisphere.

- On a clear night, you can see the long shape of Hydra stretching across the sky.
- Hydra is notable not only for its immense size but also for containing several interesting deep-sky objects, including the Ghost of Jupiter nebula.

## Examples

- 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.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.