Hill's partner (4)
I believe the answer is:
dale
'hill's partner' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for dale that I've seen before include "Valley; Trollope's Bell and Lily" , "Lead into poetic valley" , "Up hill and down . . . ." , "depression" , "Valley, as in Yorkshire" .)