Omen of wickedness -- there's little good in it (4)
I believe the answer is:
sign
'omen' is the definition.
(I've seen this in another clue)
'wickedness there's little good in it' is the wordplay.
'wickedness there' becomes 'sin' (I can't justify this - if you can you should give a lot more credence to this answer).
'little' suggests taking the first letters.
'in it' is an insertion indicator.
The initial letter of 'good' is 'g'.
'sin' going around 'g' is 'SIGN'.
'of' is the link.
Can you help me to learn more?
(Other definitions for sign that I've seen before include "Authorise with a name" , "Communicate to the deaf" , "Public notice; portent" , "Endorse" , "Evidence" .)