Taking off, having snatched cover from coffin? That’s dreadful (9)
I believe the answer is:
appalling
'that's dreadful' is the definition.
(I've seen this before)
'taking off having snatched cover' is the wordplay.
'taking off' becomes 'aping' (both can mean imitating or mocking).
'having snatched' is an insertion indicator.
'cover' becomes 'pall' (palling is a kind of covering).
'aping' placed around 'pall' is 'APPALLING'.
'from coffin?' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for appalling that I've seen before include "Shockingly bad" , "Horrific" , "Dreadful" , "page entirely covered in copying" , "Greatly horrifying" .)