Horse starts to amble into northern part of range (8)
I believe the answer is:
mountain
'range' is the definition.
(synonyms)
'horse starts to amble into northern part' is the wordplay.
'horse' becomes 'mount' (mount is a kind of horse).
'starts to' indicates taking the first letters.
'part' indicates taking the first letters.
The initial letter of 'amble' is 'a'.
The initial letters of 'into northern' is 'in'.
'mount'+'a'+'in'='MOUNTAIN'
'of' acts as a link.
(Other definitions for mountain that I've seen before include "Big hill" , "Projecting land mass" , "Eg, K2" , "Alp" , "Something made out of a molehill?" .)