Wicked act (8)
I believe the answer is:
atrocity
'wicked act' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for atrocity that I've seen before include "Frightful act of citatory kind" , "Wickedness" , "monstrous crime" , "Barbarous, inhuman act" , "Barbarity, inhumanity" .)