Spring open (5)

I believe the answer is:

start

I believe this is a double definition.

'spring' is the first definition.
(thesaurus)

'open' is the second definition.
(thesaurus)

(Other definitions for start that I've seen before include "Move quickly < when surprised" , "Begin with sudden movement of surprise" , "launch" , "Set in motion" , "Outset" .)

I've seen this clue in the Evening Standard.

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