The most common and most likely answer to this crossword clue is the 8 letter word WATCHMAN
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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 WATCHMAN mean?
WATCHMAN noun- One set to watch; a person who keeps guard, especially one who guards a building, or the streets of a city, by night.