Body part producing argon (5)
I believe the answer is:
organ
'body part' is the definition.
(I know that organ is a type of body part)
'producing argon' is the wordplay.
'producing' indicates anagramming the letters.
'argon' with letters rearranged gives 'ORGAN'.
(Other definitions for organ that I've seen before include "Mouthpiece" , "Agency" , "ear maybe" , "Eg, heart, liver" , "with a lofty tone?" .)