Spring, effectively (4)

I believe the answer is:

well

This clue is a double definition.

'spring' is the first definition.
(thesaurus)

'effectively' is the second definition.
(thesaurus)

(Other definitions for well that I've seen before include "Healthy - water supply" , "Underground source" , "Fit and healthy" , "Extremely; plentiful supply" , "Very; deep shaft" .)

I've seen this clue in The Times.

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