Area covered by Scottish hill runner, perhaps (4)
I believe the answer is:
bean
'runner perhaps' is the definition.
'area covered by scottish hill' is the wordplay.
'area' becomes 'a' (maths abbreviation).
'covered by' means one lot of letters goes inside another.
'scottish hill' becomes 'ben' (I can't explain this - if you can you should believe this answer much more).
'a' put into 'ben' is 'BEAN'.
Can you help me to learn more?
(Other definitions for bean that I've seen before include "Vegetable; coffee seed" , "Kidney-shaped seed as for coffee" , "Seed of coffee plant" , "comic character" , "Haricot, for example" .)