Place pound inside each prison island (4)
I believe the answer is:
elba
'island' is the definition.
(Italian island)
'place pound inside each prison' is the wordplay.
I cannot really see how this works, but
'pound' could be 'lb' (abbreviation for the unit of weight) and 'lb' is present in the answer.
'each' could be 'ea' (abbreviation) and 'ea' is present in the remaining letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for elba that I've seen before include "Italian island" , "place for Napoleon" , "Italian isle" , "Island of Napoleon's exile in 1814-15" , "Abel (anag)" .)