American monk with a halo that’s slipping (9)
I believe the answer is:
Here is my best explanation:
'american' is the definition.
(I've seen this before)
'monk with a halo that's slipping' is the wordplay.
'with' is a charade indicator (letters next to each other).
'that's slipping' indicates an anagram.
'monkahalo' with letters rearranged gives 'OKLAHOMAN'.
(Other definitions for oklahoman that I've seen before include "from Tulsa?", "American" and "US resident".)