Foolish of one doctor returning diamonds left in charge (9)

I believe the answer is:

imbecilic

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'foolish' is the definition.
(thesaurus)

'of one doctor returning diamonds left in charge' is the wordplay.
'of one' becomes 'i' (I've seen this in other clues).
'doctor' becomes 'MB' (Bachelor of Medicine, Medicinae Baccalaureus).
'returning' is a reversal indicator.
'diamonds' becomes 'ice' (slang term for diamonds).
'left in charge' becomes 'lic' (this could be a standard abbreviation I've not previously seen).
'ice' written backwards gives 'eci'.
'i'+'mb'+'eci'+'lic'='IMBECILIC'

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(Another definition for imbecilic that I've seen is " stupid".)

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

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