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' shows that the letters should be reversed in order.
'in' is an insertion indicator.
'empty' says to hollow out the word (remove centre letters).
'synagogue' with its middle taken out is 'se'.
'kip' written backwards gives 'pik'.
'pik' inserted into 'se' is 'SPIKE'.
'has' is the 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" .)