Hang ominously (4)
I believe the answer is:
loom
'hang ominously' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for loom that I've seen before include "Apparatus for weaving cloth" , "Textile machine; come into sight" , "'Appear as a vague form, perhaps threatening (4)'" , "Appear large and indistinct, to weave?" , "Impend; weaving machine" .)