It warns of a temptress (5)

I believe the answer is:

siren

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'temptress' is the definition.
(I know that temptress can be written as siren)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for siren that I've seen before include "Temptress; warning signal" , "Risen like Lorelei" , "Device making a loud wailing sound" , "Charmer" , "Alluring female" .)

I've seen this clue in the Sydney Morning Herald.

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