'omen' originates from Latin, specifically the word 'omen' (Latin 'omen'), although its ultimate origin is uncertain.

'omen' passed into Middle English from Latin 'omen' (via medieval Latin), keeping a similar form and meaning into modern English.

Initially, it meant 'a sign (often considered from the gods)', but over time it evolved into the broader modern sense of 'a sign of what will happen' (either good or bad).