Fill-in (4)
(Other definitions for stopgap that I've seen before include "Interim" , "Provisional" , "Temporary expedient" , "A temporary substitute or solution" , "Improvisation" .)
'fill-in' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for temp that I've seen before include "Short-term worker, in short" , "Non-permanent worker" , "Short-time worker" , "Short-term office worker" , "N on-permanent worker" .)