The most common and most likely answer to this crossword clue is the 8 letter word THREATEN
I've seen this crossword clue in The Times
T
H
R
E
A
T
E
N
More clues leading to the result THREATEN
- Loom yarn cut meshed fabric backing
- Look likely to have small card briefly over a higher one
- Number going round at noon are menacing
- Indicate danger of reconstructing New Theatre
- Endanger trio sheltering at noon
- Mad Hatter points to cow
- Menace near the front of tent, moving
- Cut yarn number in loom
- Hear tent shaking - to suggest rain?
- Put the screws on X after change of heart
Buddy explains!

The straight part
We know that "loom" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case loom = threaten.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does THREATEN mean?
THREATEN verb- To make a threat against someone; to use threats.
- To menace, or be dangerous.
- To portend, or give a warning of.
- To be close to equaling or surpassing (a record, etc.)