Mafia boss hiding gun parts and drug in prison (7)
I believe the answer is:
dungeon
'prison' is the definition.
(thesaurus)
'mafia boss hiding gun parts and drug' is the wordplay.
'mafia boss' becomes 'don' (I've seen this before).
'hiding' is an insertion indicator.
'parts' is an anagram indicator (the parts of the original word ordered differently).
'and' is a charade indicator (letters next to each other).
'drug' becomes 'e' (e is another name for ecstasy).
'gun' anagrammed gives 'ung'.
'ung'+'e'='unge'
'don' going around 'unge' is 'DUNGEON'.
'in' is the link.
(Other definitions for dungeon that I've seen before include "Prison cell, often underground" , "Eg, the Black Hole of Calcutta" , "Underground prison-cell" , "Uncongenial accommodation" , "prison the result" .)