Regions of dry and rocky hills (7)
I believe the answer is:
sectors
'regions' is the definition.
(I know this)
'dry and rocky hills' is the wordplay.
'dry' becomes 'sec' (similar in meaning).
'and' says to put letters next to each other.
'rocky hills' becomes 'tors' (I've seen this in another clue).
'sec'+'tors'='SECTORS'
'of' is the link.
(Other definitions for sectors that I've seen before include "mathematical instruments" , "Divisions of a nation's economic operations" , "Branches of enterprise" .)