Requirement to fix rot in rice (9)
I believe the answer is:
criterion
'requirement' is the definition.
The definition and answer can be both related to thinking as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'fix rot in rice' is the wordplay.
'fix' is an anagram indicator.
'rot'+'in'+'rice'='rotinrice'
'rotinrice' with letters rearranged gives 'CRITERION'.
'to' is the link.
Can you help me to learn more?
(Other definitions for criterion that I've seen before include "London theatre?" , "Standard by which to judge" , "Standard by which something can be judged" , "Standard; model" , "Judging standard" .)