Panic as fierce aggressor is eviscerated (4)
I believe the answer is:
fear
'panic' is the definition.
(I know that panic is a more specific form of fear)
'fierce aggressor is eviscerated' is the wordplay.
'fierce' becomes 'fe' (I can't explain this - if you can you should give a lot more credence to this answer).
'is eviscerated' suggests removing the centre (the word is disembowelled of its inside letters).
'aggressor' with its centre taken out is 'ar'.
'fe'+'ar'='FEAR'
'as' is the link.
Can you help me to learn more?
(Other definitions for fear that I've seen before include "Apprehension" , "Anxiety caused by danger" , "Qualms" , "Cutting edge" , "Be afraid of" .)