means a sign or event regarded as a warning or prophecy of something good or bad to come.

from Straight from Latin 'omen,' a word for a prophetic sign — though the Romans themselves weren't quite sure where it came from. One old guess links it to 'audire,' to hear, hinting at an omen as something whispered by the gods; that connection is uncertain. The Romans took omens very seriously, employing augurs to read the flight of birds and the entrails of sacrificed animals, and from that same root grew 'ominous' — the omen's gloomier cousin.