To the ruling head, a high place (3)
I believe the answer is:
tor
'a high place' is the definition.
(I've seen this in another clue)
'to the ruling head' is the wordplay.
'head' suggests taking the first letters.
The initial letter of 'ruling' is 'r'.
'to'+'r'='TOR'
(Other definitions for tor that I've seen before include "A rocky hill in Devon" , "Rot on a hill in Devon" , "Hill or rocky peak" , "Pillar of rock" , "Feature of Dartmoor" .)