Dear former partner in a brown study (9)

I believe the answer is:

expensive

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'dear' is the definition.
(similar in meaning)

'former partner in a brown study' is the wordplay.
'former partner' becomes 'ex' (an ex-partner).
'in a brown study' becomes 'pensive' (I can't justify this - if you can you should believe this answer much more).
'ex'+'pensive'='EXPENSIVE'

Can you help me to learn more?

(Other definitions for expensive that I've seen before include "Very costly or dear" , "not going for a song" , "High in price" , "priceless" , "Highly-priced" .)

I've seen this clue in the Sydney Morning Herald.

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