Endless feud over money causing concern (4)

I believe the answer is:

firm

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'concern' is the definition.
(firm is a kind of concern)

'endless feud over money' is the wordplay.
'endless feud over' becomes 'fir' (I can't justify this - if you can you should believe this answer much more).
'money' becomes 'm' (abbreviation in economics).
'fir'+'m'='FIRM'

'causing' is the link.

Can you help me to learn more?

(Other definitions for firm that I've seen before include "A steady business enterprise? (4)" , "Steady commercial organisation?" , "Resistant to pressure" , "Hard" , "Stable; business" .)

I've seen this clue in The Hindu.

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