Groan, using gas (5)
I believe the answer is:
argon
'gas' is the definition.
(argon is a gas)
'groan using' is the wordplay.
'using' indicates an anagram (the letters used in a different way).
'groan' with letters rearranged gives 'ARGON'.
(Other definitions for argon that I've seen before include "elementary" , "noble element" , "Gaseous element" , "Noble gas used in light bulbs" , "Inert eighteen ac gas" .)