Jazzy organ is a gas (5)
I believe the answer is:
argon
'gas' is the definition.
(argon is a gas)
'jazzy organ' is the wordplay.
'jazzy' is an anagram indicator.
'organ' is an anagram of 'ARGON'.
'is a' is the link.
(Other definitions for argon that I've seen before include "Inert gas, symbol Ar" , "Inert gas, present in small amounts in the air" , "Organ (anag.)" , "Gas, inert constituent of air" , "Gas used in electric lights" .)