Cool criminal in capital of Sicily, Palermo (10)
I believe the answer is:
'cool' is the definition.
(I've seen this before)
'criminal in capital of sicily palermo' is the wordplay.
'criminal' indicates anagramming the letters.
'capital of' indicates taking the first letters.
The initial letter of 'sicily' is 's'.
'inspalermo' is an anagram of 'IMPERSONAL'.
(Other definitions for impersonal that I've seen before include "Aloof" , "Objective; disinterested" , "Cool" , "Cold" , "Ignoring one's own feelings" .)