The fellow protected by idiot remains (5)
I believe the answer is:
ashes
'remains' is the definition.
(thesaurus)
'the fellow protected by idiot' is the wordplay.
'the fellow' becomes 'he' (I've seen this in other clues).
'protected by' is an insertion indicator.
'idiot' becomes 'ass' (I've seen this before).
'he' put inside 'ass' is 'ASHES'.
(Other definitions for ashes that I've seen before include "` `..... to ....., dust to dust' ' (prayer)" , "Embers" , "Eng/Aus test series" , "trees" , "Burnt residue" .)