Profligate vacation's ending in French city (5)
I believe the answer is:
rouen
'french city' is the definition.
(I've seen this before)
'profligate vacation's ending' is the wordplay.
'profligate' becomes 'roue' (synonyms).
'ending' indicates one should take the final letters (the letter at the end of the word).
The last letter of 'vacation' is 'n'.
'roue'+'n'='ROUEN'
'in' acts as a link.
(Other definitions for rouen that I've seen before include "Port on river Seine" , "City in northern France" , "Cathedral city, capital of Normandy" , "French port" , "French community" .)