American monk with a halo that’s slipping (9)
I believe the answer is:
oklahoman
'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.
'monk'+'a'+'halo'='monkahalo'
'monkahalo' with letters rearranged gives 'OKLAHOMAN'.
(Other definitions for oklahoman that I've seen before include "from Tulsa?" , "American" , "US resident" .)