Vixen only has gas (5)
I believe the answer is:
xenon
'gas' is the definition.
(I've seen this before)
'vixen only has' is the wordplay.
'has' indicates the answer is hidden within the clue.
'XENON' is hidden within 'vixen only'.
(Other definitions for xenon that I've seen before include "Inert gas, Xe" , "Gaseous element, Xe" , "One of the noble set" , "member of nobility?" , "One of the noble gasses" .)