Money which is tied up in poisons (9)

I believe the answer is:

banknotes

I'm a little stuck... Click here to teach me more about this clue!

'money' is the definition.
(thesaurus)

'tied up in poisons' is the wordplay.
'tied up' becomes 'knot' (I can't explain this - if you can you should believe this answer much more).
'in' is an insertion indicator.
'poisons' becomes 'banes' (I've seen this in another clue).
'knot' placed inside 'banes' is 'BANKNOTES'.

'which is' is the link.

Can you help me to learn more?

(Another definition for banknotes that I've seen is " 1a [money]".)

I've seen this clue in The Independent.

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