One properly drilled? (4)
I believe the answer is:
well
'one properly' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for well that I've seen before include "four-letter word repeated in Shakespeare comedy" , "Cockpit" , "run" , "Issue forth" , "satisfactory manner?" .)