None used element (4)
I believe the answer is:
neon
'element' is the definition.
(I know that neon is a type of element)
'none used' is the wordplay.
'used' indicates an anagram.
'none' with letters rearranged gives 'NEON'.
(Other definitions for neon that I've seen before include "One of the six inert gases" , "Gas used in fluorescent lamps" , "Small plant; colour" , "Inert gas, symbol Ne" , "illuminating agent" .)