Point in question raised by farmer (5)
I believe the answer is:
wheat
'farmer' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'point in question raised by' is the wordplay.
'point' becomes 'W' (West).
'in question' becomes 'eh' (I can't justify this - if you can you should give a lot more credence to this answer).
'raised' shows that the letters should be reversed in order (going up in a down clue).
'by' becomes 'at'.
'eh' backwards is 'he'.
'w'+'he'+'at'='WHEAT'
Can you help me to learn more?
(Other definitions for wheat that I've seen before include "Source of flour" , "Grass whose grain is used to make flour" , "Cereal grain" , "Cereal crop" , "Type of cereal" .)