Doctor has to sleep over in empty synagogue (5)
I believe the answer is:
spike
'doctor' is the definition.
(I've seen this before)
'to sleep over in empty synagogue' is the wordplay.
'to sleep' becomes 'kip' ('kip' can be a synonym of 'sleep').
'over' is a reversal indicator.
'in' is an insertion indicator.
'empty' means to remove the middle letters.
'synagogue' with its middle removed is 'se'.
'kip' in reverse letter order is 'pik'.
'pik' inserted inside 'se' is 'SPIKE'.
'has' acts as a link.
(Other definitions for spike that I've seen before include "Thin point; -- Milligan" , "add something to it" , "one that may be found on running shoe" , "Doctor" , "Sharp point; flower cluster" .)