Hardy monster, being difficult to decapitate? (5)
I believe the answer is:
hydra
'hardy monster' is the definition.
'Hydra' can be an answer for 'monster' (I've seen this before). I am not sure about the 'hardy' bit.
'being difficult to decapitate?' is the wordplay.
I cannot quite see how this works, but
'being' could be 'dr' (Dr is an example) and 'dr' is located in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for hydra that I've seen before include "Many-headed foe of Hercules" , "Many-headed snake slain by Hercules" , "M any-headed monster fought by Hercules" , "Mythological monster with nine heads" , "Water monster" .)