Hardy monster? (5)

I believe the answer is:

hydra

I'm a little stuck... Click here to teach me more about this clue!

'monster?' is the definition.
(Hydra is an example)

'hardy' is the wordplay.
'hardy' can be anagrammed to 'HYDRA'.
Though, I am unsure how this is indicated.

Can you help me to learn more?

(Other definitions for hydra that I've seen before include "M any-headed monster fought by Hercules" , "Many-headed foe of Hercules" , "Mythical many-headed snake" , "Mythological monster with nine heads" , "Nine-headed monster killed by Hercules" .)

I've seen this clue in the Evening Standard.

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