Manure one spread in pen? (7)
I believe the answer is:
dungeon
'pen?' is the definition.
(thesaurus)
'manure one spread in' is the wordplay.
'manure' becomes 'dung' (I've seen this before).
'spread' is an anagram indicator.
'in' is an insertion indicator.
'one' is an anagram of 'eon'.
'dung' placed inside 'eon' is 'DUNGEON'.
(Other definitions for dungeon that I've seen before include "Place of confinement underground" , "Dark place of confinement" , "Dark underground cell for prisoners" , "prison the result" , "Unpleasant cell" .)