Unholy fiend wiping brow (4)
I believe the answer is:
evil
'unholy' is the definition.
(I've seen this in another clue)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for evil that I've seen before include "Villainy" , "Live kind of badness" , "Extremely wicked" , "Depravity, wickedness" , "heinous" .)