One inside wards off evil spirits (6)
I believe the answer is:
fiends
'evil spirits' is the definition.
(I know that daemon is a subclass of evil disembodied spirit)
'one inside wards off' is the wordplay.
'one' becomes 'i' (Roman numeral).
'inside' is an insertion indicator.
'wards off' becomes 'fends' (I've seen this in another clue).
'i' going inside 'fends' is 'FIENDS'.
(Other definitions for fiends that I've seen before include "Very wicked or cruel people" , "Demons or devils" , "Devils or cruel people" , "Cruel, wicked and inhuman persons" , "Devils, monsters" .)