One properly drilled, presumably (4)

I believe the answer is:

well

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'one properly' is the definition.
(thesaurus)

I don't understand how the rest of the clue works.

(Other definitions for well that I've seen before include "Bore; extremely" , "Profoundly" , "Very much; plentiful source or supply" , "Healthy; extremely" , "Abundant source" .)

I've seen this clue in the Evening Standard.

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