Doctor's surgery in decline (4)

I believe the answer is:

drop

I'm a little stuck... Click here to teach me more about this clue!

'decline' is the definition.
(I know that drop is a type of decline)

I cannot understand how the rest of the clue works.

(Other definitions for drop that I've seen before include "sack" , "Sweet; fall" , "Pendant earring" , "Fall; abandon" , "Finish with" .)

I've seen this clue in The Sun.

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