Threaten to come to a devilish conclusion (6)
I believe the answer is:
impend
'threaten' is the definition.
(I've seen this before)
'devilish conclusion' is the wordplay.
'devilish' becomes 'imp' (I've seen this in other clues).
'conclusion' becomes 'end' (something's conclusion is its end).
'imp'+'end'='IMPEND'
'to come to a' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for impend that I've seen before include "Threaten - be about to happen" , "(Of a bad thing) loom" , "Be about to take place" , "Threaten; approach" , "Be looming" .)