Menace -- weaver? (4)
I believe the answer is:
loom
I believe this is a double definition.
'menace' is the first definition.
(thesaurus)
'weaver?' is the second definition.
(thesaurus)
(Other definitions for loom that I've seen before include "'Appear as a vague form, perhaps threatening (4)'" , "Appear large and indistinct, to weave?" , "Appear indistinctly, in threatening form" , "Apparatus for weaving cloth" , "Rise up threateningly ahead" .)