River bend with profundity (6)

I believe the answer is:

deeply

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'with profundity' is the definition.
(I've seen this before)

'river bend' is the wordplay.
'river' becomes 'Dee' (River Dee).
'bend' becomes 'ply' (I can't justify this - if you can you should give a lot more credence to this answer).
'dee'+'ply'='DEEPLY'

Can you help me to learn more?

(Other definitions for deeply that I've seen before include "In a profound way" , "Thoroughly" , "Profoundly" , "With profundity" , "With intense feeling" .)

I've seen this clue in The Independent.

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