Endpoint of failing memory: to damage language structure (7)
I believe the answer is:
grammar
'language structure' is the definition.
The definition and answer can be both related to thinking as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'endpoint of failing memory to damage' is the wordplay.
'endpoint of failing memory' becomes 'gram' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'to damage' becomes 'mar' (to mar is to spoil or damage).
'gram'+'mar'='GRAMMAR'
Can you help me to learn more?
(Other definitions for grammar that I've seen before include "Study of basic linguistic units" , "Branch of linguistics that deals with syntax" , "type of school" , "A language's syntax and morphology" , "Correct usage of words" .)