Cycle around grand hilltop (5)
I believe the answer is:
ridge
'hilltop' is the definition.
(I've seen this before)
'cycle around grand' is the wordplay.
'cycle' becomes 'ride' (ride can mean to ride a bike).
'around' indicates putting letters inside.
'grand' becomes 'g' (G is short for grand as in a thousand).
'ride' placed around 'g' is 'RIDGE'.
(Other definitions for ridge that I've seen before include "Top of a long narrow hill" , "Long, narrow range of hills" , "Long mountain crest or roof life" , "Crest - reef" , "Narrow hill-range" .)