Corny, perhaps, but not much? (5)
I believe the answer is:
grain
'much?' is the definition.
The answer and definition can be both quantities as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for grain that I've seen before include "Enter into combat with" , "Small hard particle of anything" , "Pattern of lines in wood" , "Cereal crops" , "Single piece of sand etc" .)