The most common and most likely answer to this crossword clue is the 5 letter word JUDAS
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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 JUDAS mean?
JUDAS noun- A traitor; a person not to be trusted.
- A small hole in a door through which a person can spy without being seen from the other side, used especially in prisons; a Judas-hole.