Crossword Genius

Problem with symbol that can’t be gone back over (7)

Ross

I believe the answer is:

rubicon

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'problem with symbol that can't be gone back over' 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?

'problem with symbol' is the wordplay.
'problem' becomes 'rub' (the rub can mean a problem or catch).
'with' says to put letters next to each other.
'symbol' becomes 'icon' (I've seen this in another clue).
'rub'+'icon'='RUBICON'

Can you help me to learn more?

(Other definitions for rubicon that I've seen before include "Line fatefully gone over" , "Caesar crossed this river in an irreversible step" , "Cross it to pass the point of no return" , "Caesar's point of no return" , "Caesar got over this" .)

I've seen this clue in The Times.
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