Organ producing gas (5)
I believe the answer is:
argon
'gas' is the definition.
(argon is a gas)
'organ producing' is the wordplay.
'producing' indicates an anagram.
'organ' anagrammed gives 'ARGON'.
(Other definitions for argon that I've seen before include "An insert gas to groan about" , "Chemical element" , "Inert gas, present in small amounts in the air" , "something inert and insubstantial" , "Noble gas, Ar" .)