Put up with, when one harped on (5)

I believe the answer is:

dwelt

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'harped on' is the definition.
'dwelt' can be an answer for 'harped' (I've seen this in another clue). I am not sure about the 'on' bit.

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for dwelt that I've seen before include "Remained" , "Lived (in a place)" , "lodged" , "Lived, resided" , "Had house" .)

I've seen this clue in the Evening Standard.

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