Crossword Genius

Diabolically (10)

Ross

I believe the answer is:

fiendishly

'diabolically' is the definition.
(I know that diabolically can be written as fiendishly)

This is all the clue.

(Another definition for fiendishly that I've seen is " Infernally clever".)

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