Criminal Cain out? Vigilance needed (7)

I believe the answer is:

caution

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'vigilance needed' is the definition.
I can't judge whether this definition defines the answer.

'criminal cain out?' is the wordplay.
'criminal' indicates an anagram.
'cain'+'out'='cainout'
'cainout' is an anagram of 'CAUTION'.

Can you help me to learn more?

(Other definitions for caution that I've seen before include "Admonish - warning" , "Caveat, prudence" , "Heed - warning - funny person" , "amusing type" , "Warning - prudence" .)

I've seen this clue in The Sun.

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