Gangster cuts lad in parlour (5)
I believe the answer is:
salon
'parlour' is the definition.
(salon is a kind of parlour)
'gangster cuts lad' is the wordplay.
'gangster' becomes 'al' (Al Capone).
'cuts' is an insertion indicator (some letters cut their way into other letters).
'lad' becomes 'son' (lad can informally mean a young boy).
'al' inserted inside 'son' is 'SALON'.
'in' acts as a link.
(Other definitions for salon that I've seen before include "Hairdresser's premises" , "Drawing room" , "Elegant room - for hairdresser?" , "where cuts are commonplace" , "Parisian art exhibition" .)