Formerly thoughtful, dear? (9)
I believe the answer is:
expensive
'dear?' is the definition.
(I've seen this before)
'formerly thoughtful' is the wordplay.
'formerly' becomes 'ex'.
'thoughtful' becomes 'pensive' ('pensive' can be similar in meaning to 'thoughtful').
'ex'+'pensive'='EXPENSIVE'
(Other definitions for expensive that I've seen before include "priceless" , "not going for a song" , "Charging a lot" , "Costing a lot of money" , "High in price" .)