Body part generating argon (5)
I believe the answer is:
organ
'body part' is the definition.
(I know that organ is a type of body part)
'generating argon' is the wordplay.
'generating' indicates an anagram (I've seen 'generated' mean this).
'argon' is an anagram of 'ORGAN'.
(Other definitions for organ that I've seen before include "notes issue from this" , "Word after "pipe" or "barrel"" , "Perhaps one that's stopped" , "Part with special function" , "Biological functionary" .)