Appear to understand source of malevolence (4)
I believe the answer is:
seem
'appear' is the definition.
('seem' can be a synonym of 'appear')
'understand source of malevolence' is the wordplay.
'understand' becomes 'see' ('see' can be a synonym of 'understand').
'source of' says to take the initial letters.
The first letter of 'malevolence' is 'm'.
'see'+'m'='SEEM'
'to' is the link.
(Other definitions for seem that I've seen before include "Come across as" , "Appear, give impression of being" , "Appear, look" , "Appear to the eye" .)