Covering evil operation (4)
I believe the answer is:
veil
'covering' is the definition.
(veil is a kind of covering)
'evil operation' is the wordplay.
'evil' anagrams to 'VEIL'.
Though, I'm not sure how this is indicated.
Can you help me to learn more?
(Other definitions for veil that I've seen before include "Transparent face cover" , "Nun's headdress" , "Fabric face covering" , "Nun's head-covering" , "Yashmak, e.g." .)