Appear ominously (4)
I believe the answer is:
loom
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">appear ominously</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for loom that I've seen before include "Weaving instrument" , "Weaving machine to appear indistinctly" , "tower" , "Textile machine for weaving" , "Machine for weaving yarn" .)