Element damaging organ (5)
I believe the answer is:
argon
'element' is the definition.
(argon is a kind of element)
'damaging organ' is the wordplay.
'damaging' indicates anagramming the letters.
'organ' anagrammed gives 'ARGON'.
(Other definitions for argon that I've seen before include "An insert gas to groan about" , "Inert gas, present in small amounts in the air" , "Gaseous element" , "Noble gas, atomic number 18" , "Inert gas, symbol Ar" .)