Weaving apparatus (4)
I believe the answer is:
'weaving apparatus' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for loom that I've seen before include "Weaving machine to appear indistinctly" , "menacing" , "'Appear as a vague form, perhaps threatening (4)'" , "textile manufacturer" , "Apparatus for weaving cloth" .)