Evil sort of mask (4)
I believe the answer is:
veil
'mask' is the definition.
(I've seen this before)
'evil sort' is the wordplay.
'sort' is an anagram indicator.
'evil' anagrammed gives 'VEIL'.
'of' acts as a link.
(Other definitions for veil that I've seen before include "Transparent face cover" , "Face-covering for brides and other women" , "Concealing material" , "Bridal headdress" , "Conceal, screen" .)