Hardy monster, being difficult to decapitate? (5)
I believe the answer is:
Here is my best explanation:
'hardy monster' is the definition.
'Hydra' can be an answer for 'monster' (Hydra is an example). I am not sure about the 'hardy' bit.
'being difficult to decapitate?' is the subsidiary indication.
I cannot quite understand how this works, but
'being' could be 'dr' (Dr is an example) and 'dr' is present in the answer.
This explanation may well be incorrect...
(Other definitions for hydra that I've seen before include "Mythological water-monster", "Femme fatale of legend", "Mythic monster with nine heads", "Monster Hercules slew", "Mythological monster with nine heads", "Nine-headed monster of Greek myth", "Mythical many-headed snake", "Water-monster", "Proliferating-head monster" and "Persistent trouble".)