Crossword Genius

Singular noun that, when a "w" is added to the front, becomes a plural noun (4)

Ross

I believe the answer is:

omen

(Other definitions for omen that I've seen before include "Foreboding" , "Sign of things to come" , "Forecast" , "Sign of something about to happen" , "Augur" .)

I've seen this clue in The New York Times.
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