Gangster loses one item of clothing (3)
I believe the answer is:
cap
'item of clothing' is the definition.
'gangster loses one' is the wordplay.
'gangster' becomes 'capone' (Al Capone).
'loses' indicates named letters should be taken away.
'capone' with 'one' removed is 'CAP'.
(Other definitions for cap that I've seen before include "Soft hat; crown" , "Stopper" , "Flat brimless hat" , "Seal off oil-well" , "'If the . . . fits, wear it' (3" .)