Old love knitted nice top that proves rule? (9)
I believe the answer is:
exception
'love knitted nice top that proves rule?' is the definition.
The definition and answer can be both related to thinking as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'old' is the wordplay.
I cannot quite understand how this works, but
'old' could be 'ex' (prefix meaning former or onetime) and 'ex' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for exception that I've seen before include "It doesn't conform to the general rule" , "Something not conforming to a rule" , "The one that proves the rule" , "Something not following a rule" , "what's against the rules" .)