Gas produced by an organ (5)
I believe the answer is:
argon
'gas' is the definition.
(argon is a gas)
'by an organ' is the wordplay.
'organ' anagrams to 'ARGON'.
Though, I am not clear how this is indicated.
'produced' is the link.
Can you help me to learn more?
(Other definitions for argon that I've seen before include "noble element" , "Inert gas in atmosphere" , "Organ (anag.)" , "Inert gas, symbol Ar" , "rare gas" .)