Doctor saving a space (3)
I believe the answer is:
gap
'space' is the definition.
(gap is a kind of space)
'doctor saving a' is the wordplay.
'doctor' becomes 'gp' (general practitioner**).
'saving' means one lot of letters goes inside another.
'gp' going around 'a' is 'GAP'.
(Other definitions for gap that I've seen before include "A break or opening as in a hedge" , "Interval, break" , "Interval, space" , "Break, in a fence say" , "Pause" .)