Develop a way through the Scottish mountain (7)
I believe the answer is:
broaden
'develop' is the definition.
(thesaurus)
'a way through the scottish mountain' is the wordplay.
'a way' becomes 'road' (road is a kind of way).
'through' means one lot of letters goes inside another (inserted letters go through the word).
'the scottish mountain' becomes 'ben' (Scottish term for a peak, eg Ben Nevis).
'road' going within 'ben' is 'BROADEN'.
(Other definitions for broaden that I've seen before include "Widen" , "Extend" , "Make wider" , "Make wide or liberal, perhaps the mind" , "Stretch" .)