Crossword Genius

Monster in filthy drain (5)

Ross

I believe the answer is:

hydra

'monster' is the definition.
(I've seen this before)

'in filthy drain' is the wordplay.
'in' indicates a hidden word.
'HYDRA' is hidden within 'filthy drain'.

(Other definitions for hydra that I've seen before include "Greek island" , "Femme fatale of legend" , "Mythological monster with nine heads" , "Stars" , "Many-headed monster of Greek mythology" .)

I've seen this clue in The Guardian.
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