omen=ουσ. οιωνός, "σημάδι", προμήνυμα: bad omen κακός οιωνός, κακό σημάδι
Synonyms: augury, auspice, bodement, boding, foreboding, foretoken, harbinger, indication, portent, premonition, presage, prognostic, prognostication, prophecy, straw, warning, writing on the wall
Notes: omen has a negative connotation, a connotation absent from the word augury; generally, augury bodes well for the future, an omen bodes ill
a harbinger is an indication of the approach of something or someone; a messenger is a person who carries a communications or performs an errand; an omen is a sign of something about to happen