Hills of windblown sand (5)
I believe the answer is:
dunes
'hills of windblown sand' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for dunes that I've seen before include "lots of sand" , "Nudes behind sand-hills" , "beach" , "Sand hills by the sea" , "Hills of windblown sand" .)