Portentous sign (4)

I believe the answer is:

omen

'portentous sign' is the definition.
(I've seen this in another clue)

This is all the clue.

(Other definitions for omen that I've seen before include "Straw in the wind" , "Augur" , "Harbinger, augury" , "premonition" , "Prognostication" .)

I've seen this clue in the USA Today, the Wall Street Journal, the Universal, The Guardian and the King Feature Syndicate.

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