The holiest city of Islam (5)
I believe the answer is:
mecca
'the holiest city of islam' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for mecca that I've seen before include "Islam's holiest city" , "Birthplace of the Prophet Mohammed" , "Moslem holy city" , "Joint capital of Saudi Arabia" , "City in Saudi Arabia, chief place of Muslim pilgrimage" .)