Infernal? Not at all! (4,4)
I believe the answer is:
like hell
'not at all' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for like hell that I've seen before include "What a masochist might do" , "No way" , "recklessly" , "very quickly" .)