As frightening as a backdraught would be (5-8)
I believe the answer is:
spine-chilling
'frightening as a backdraught would be' is the definition.
I can't tell whether this definition defines the answer.
'as' is the wordplay.
I cannot really see how this works, but
'as' could be 'in' (I've seen this in other clues) and 'in' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for spine-chilling that I've seen before include "Bloodcurdling" , "Arousing terror" , "Inspiring both terror and excitement" , "Scary" , "Terrifying" .)