Fearful, but again subject to uncertainty? (11)

I believe the answer is:

redoubtable

This clue is a double definition.

'fearful' is the first definition.
(thesaurus)

'again subject to uncertainty?' is the second definition.
(able to be doubted again)

'but' is the link.

(Other definitions for redoubtable that I've seen before include "Fearsome - unnerving" , "Formidable" .)

I've seen this clue in The Times.

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