New road, new element (5)
I believe the answer is:
radon
'element' is the definition.
(radon is a kind of element)
'new road new' is the wordplay.
'new' is an anagram indicator.
'new' becomes 'n' (**).
'road' with letters rearranged gives 'rado'.
'rado'+'n'='RADON'
(Other definitions for radon that I've seen before include "Element, symbol Rn" , "Inert gas that occurs naturally" , "gets no reaction" , "Rare noble gas" , "Natural gas considered a hazard to health" .)