"The City of Light" (5)
I believe the answer is:
paris
'the city of light' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for paris that I've seen before include "investment resulted from his action" , "French department" , "City; Juliet's betrothed Count" , "Prince who abducted Helen, starting a long war (see 8)" , "Arc de Triomphe city" .)