Discontented boffin accepts argument that cereal is full of fibre (5,4)
I believe the answer is:
brown rice
'full of fibre' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'discontented boffin accepts argument that cereal' is the wordplay.
'discontented' says to hollow out the word (remove centre letters) (the word's contents are removed).
'accepts' means one lot of letters goes inside another.
'argument' becomes 'row' (to row is to argue).
'that cereal' becomes 'rice' (rice is a kind of cereal).
'boffin' with its middle taken out is 'bn'.
'bn' enclosing 'row' is 'brown'.
'brown'+'rice'='BROWN RICE'
'is' is the link.
Can you help me to learn more?
(Other definitions for brown rice that I've seen before include "Health food" , "Dark grains" , "Unpolished food grains" .)