Prevents movement near the western borders (6)
I believe the answer is:
wedges
'prevents movement' is the definition.
I can't judge whether this defines the answer.
'near the western borders' is the wordplay.
'near' means one lot of letters go next to another.
'the western' becomes 'w'.
'borders' becomes 'edges' ('edge' can be a synonym of 'border').
'w' next to 'edges' is 'WEDGES'.
Can you help me to learn more?
(Other definitions for wedges that I've seen before include "Shoves in between other objects, packs tightly" , "Golf irons with weighted heads and angled faces" , "Thrusts or packs tightly among other things" , "They taper to a thin edge" , "Chunks" .)