Nude running on hill (4)
I believe the answer is:
dune
'hill' is the definition.
(I know that dune is a type of hill)
'nude running' is the wordplay.
'running' indicates an anagram.
'nude' anagrammed gives 'DUNE'.
'on' is the link.
(Other definitions for dune that I've seen before include "Sandy hill" , "Low hill of sand, called in a desert a barkhan" , "Sandhill" , "Mound of drifted sand" , "Ridge of wind-blown sand" .)