Harbinger (4)
'harbinger' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for omen that I've seen before include "Prophetic significance" , "Augury, portent" , "Portent, prophetic indicator" , "Sign of something to come" , "Event regarded as a prophetic sign of good or evil" .)
'harbinger' is the definition.
(synonyms)
This is all the clue.
(Other definitions for herald that I've seen before include "Proclaimer" , "Official crier or messenger" , "Harbinger, messenger" , "Announce, presage" , "and 14: 'Hark! The -- -- sing' (carol)" .)