Reform apt in a lone Italian citizen (10)
I believe the answer is:
neapolitan
'italian citizen' is the definition.
(I've seen this before)
'reform apt in a lone' is the wordplay.
'reform' is an anagram indicator (letters in a new form).
'apt'+'in'+'a'+'lone'='aptinalone'
'aptinalone' with letters rearranged gives 'NEAPOLITAN'.
(Other definitions for neapolitan that I've seen before include "Italian citizen" , "Italian native" , "From Naples" , "21 [ITALIAN]" , "One coming from Campania" .)