Amount of corn perhaps that’s not known for so long? (5)
I believe the answer is:
years
'long?' is the definition.
(thesaurus)
'amount of corn perhaps that's not known for' is the wordplay.
I cannot really understand how this works, but
'amount' could be 's' (S is an example) and 's' is present in the answer.
'corn' could be 'ear' (an ear is a piece of corn) and 'ear' is found within the answer.
A single letter 'y' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
'so' is the link.
Can you help me to learn more?
(Other definitions for years that I've seen before include "12 month periods" , "Units of time" , "Ages" , "long period" , "Very long time (colloq.)" .)