Hi,
What is the difference between these two nouns
These can sometimes be interchanged, but here are a general few comments about differences.
presage Can be a feeling that you have, that some event is coming.
omen Usually a thing or an event that suggests either good or evil is coming.
You might also want to look at portent in your dictionary.
'Omen' is by far the most common of these words.
Best wishes, Clive