The most common and most likely answer to this crossword clue is the 7 letter word GORGONS
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The straight part
We know that "Monsters" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case monsters = gorgons.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 GORGONS mean?
GORGONS noun- A vicious female monster from Greek mythology with sharp fangs and hair of living, venomous snakes. One of the three sisters: Medusa, Stheno and Euryale
- An intimidating, ugly, or disgusting woman; anything hideous or horrid.