An opening in surgery (7)
I believe the answer is:
keyhole
This clue is a double definition.
'an opening' is the first definition.
(keyhole is a kind of opening)
'surgery' is the second definition.
(I've seen this before)
'in' is the link.
(Other definitions for keyhole that I've seen before include "Aperture in lock - kind of surgery" , "Opening in door etc" , "Opening in door - kind of surgery" , "may cover a number of wards" , "Aperture for lock opening" .)