Mostly wealthy, with a good deal of passion for American economist (7)

'economist' is the definition.
(I've seen this before)

'mostly wealthy with a good deal of' is the wordplay.
'mostly' means to remove the last letter (most but not all of the word).
'wealthy' becomes 'rich' (similar in meaning).
'with' means one lot of letters go next to another.
'good deal' becomes 'rd' (I can't justify this - if you can you should give a lot more credence to this answer).
'of' becomes 'o''.
'rich' with its last letter removed is 'ric'.
'ric'+'a'+'rd'+'o'='RICARDO'

'passion for american' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.

Can you help me to learn more?