Rolling, as terrain (5)
I believe the answer is:
hilly
'rolling as terrain' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for hilly that I've seen before include "Unlike flat land" , "Mountainous" , "Not flat (country)" , "Like Chiltern or Cotswolds areas" , "Descriptive of undulating upland" .)