Crook close to shepherd on mountain (4)
I believe the answer is:
bend
'crook' is the definition.
(synonyms)
'close to shepherd on mountain' is the wordplay.
'close to' indicates one should take the final letters (the close/ending of).
'on' says to put letters next to each other.
'mountain' becomes 'ben' (as in Ben Nevis).
The last letter of 'shepherd' is 'd'.
'd' after 'ben' is 'BEND'.
(Other definitions for bend that I've seen before include "Country; bird" , "Shape into a curve" , "Repair" , "Crouch" , "Turn - buckle" .)