Knowledge about one river (5)

I believe the answer is:

loire

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'one river' is the definition.
(Loire River is an example)

'knowledge about' is the wordplay.
'knowledge' becomes 'loi' (I can't explain this - if you can you should give a lot more credence to this answer).
'about' becomes 're' ('re' means regarding or about).
'loi'+'re'='LOIRE'

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(Other definitions for loire that I've seen before include "French department" , "flower abroad" , "Longest French river" , "French runner" , "Current French" .)

I've seen this clue in The Mirror.

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