As far as the top of the ridge, or hill (3)
I believe the answer is:
tor
'hill' is the definition.
(I know that tor is a type of hill)
'as far as the top of the ridge' is the wordplay.
'as far as' becomes 'to'.
'the top of' says to take the initial letters.
The initial letter of 'ridge' is 'r'.
'to'+'r'='TOR'
'or' acts as a link.
(Other definitions for tor that I've seen before include "(Dartmoor) rocky hill" , "feature of Glastonbury" , "A rocky hill in Devon" , "Feature of Dartmoor" , "eminence" .)