Advance booking in doubt (11)

I believe the answer is:

reservation

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This could be a double definition.

'advance booking' is the first definition.
'reservation' can be an answer for 'booking' (synonyms). I am not certain of the 'advance' bit.

'doubt' is the second definition.
(reservation is a kind of doubt)

'in' acts as a link.

Can you help me to learn more?

(Other definitions for reservation that I've seen before include "Booking (in a restaurant)" , "Expression of doubt; table booking" , "Putting aside" , "Booking - qualification" , "misgiving" .)

I've seen this clue in The Times.

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