Underworld boss, a prisoner concealing larger letters (7)
I believe the answer is:
lucifer
'underworld boss' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'a prisoner concealing larger letters' is the wordplay.
'a prisoner' becomes 'lifer' (prisoner serving a life sentence).
'concealing' indicates putting letters inside.
'larger letters' becomes 'uc' (I am not sure about this - if you are sure you should believe this answer much more).
'lifer' placed around 'uc' is 'LUCIFER'.
Can you help me to learn more?
(Other definitions for lucifer that I've seen before include "Evil spirit" , "Match - Satan" , "leader of rebellion" , "from the abyss?" , "Light" .)