Where I left a chap out (5)
I believe the answer is:
milan
'where' is the definition.
The answer is a location as well as being a singular noun. This is suggested by the definition.
'i left a chap out' is the wordplay.
'left' becomes 'L' (common abbreviation).
'a chap' becomes 'man' (chap can mean a man).
'out' means one lot of letters goes inside another.
'i'+'l'='il'
'il' put inside 'man' is 'MILAN'.
Can you help me to learn more?
(Other definitions for milan that I've seen before include "Doorstep deliverer" , "N. Italian city" , "Italian industrial city" , "town" , "European city" .)