1.
Diabolic is used to describe things that people think are caused by or belong to the Devil. (FORMAL)
...the ~ forces which lurk in all violence.
ADJ: ADJ n
2.
If you describe something as ~, you are emphasizing that it is very bad, extreme, or unpleasant. (mainly AM)
Pitt’s smile returned, and it was hideously ~.
= ~al
ADJ emphasis