Italian leader in top-security American prison (6)
I believe the answer is:
tuscan
'italian' is the definition.
(someone from Tuscany in Italy)
'leader in top-security american prison' is the wordplay.
'leader in top security' becomes 't' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'american' becomes 'us' (abbreviation for United States).
'prison' becomes 'can' (the can is American slang for prison).
't'+'us'+'can'='TUSCAN'
Can you help me to learn more?
(Other definitions for tuscan that I've seen before include "From a central Italian region" , "Person from Siena" , "Italian inhabitant of what was once Etruria" , "From a region of west central Italy" , "Relating to a region of Italy" .)