Difficulty with image that can’t be gone back over (7)
I believe the answer is:
rubicon
'difficulty with image that can't be gone back over' is the definition.
The answer and definition can be both related to thinking as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'difficulty with image' is the wordplay.
'difficulty' becomes 'rub' (rub can mean a difficulty or problem).
'with' means one lot of letters go next to another.
'image' becomes 'icon' (synonyms).
'rub'+'icon'='RUBICON'
Can you help me to learn more?
(Other definitions for rubicon that I've seen before include "win at piquet" , "Caesar got over this" , "Limit" , "ancient border" , "5 significantly crossed!" .)