City is in downward move, becoming resolute (8)

I believe the answer is:

decisive

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'resolute' is the definition.
(associated in meaning)

'city is in downward move' is the wordplay.
'city' becomes 'EC' (the City of London postcode).
'in' is an insertion indicator.
'downward move' becomes 'dive' (dive is a kind of move. I am not sure about the 'downward' bit.).
'ec'+'is'='ecis'
'ecis' going inside 'dive' is 'DECISIVE'.

'becoming' is the link.

Can you help me to learn more?

(Other definitions for decisive that I've seen before include "Settling something conclusively, as battle may be" , "Settling an issue quickly" , "Able to make up one's mind quickly and with firmness" , "Critical" , "Showing clear judgment and firmness" .)

I've seen this clue in The Times.

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