Loom (6)
I believe the answer is:
impend
'loom' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for impend that I've seen before include "appearing to be imminent" , "Threaten; approach" , "Become imminent" , "Threaten - be about to happen" , "Be imminent or about to happen" .)