The most common and most likely answer to this crossword clue is the 9 letter word WATCHWORD
I've seen this crossword clue in Independent
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More clues leading to the result WATCHWORD
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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 WATCHWORD mean?
WATCHWORD noun- A word used as a motto, as expressive of a principle, belief or rule of action; a rallying cry.
- A prearranged reply to the challenge of a sentry or a guard; a password or signal by which friends can be known from enemies.