General opposites:
* Inauspicious: This is the most direct opposite.
* Unlucky: This emphasizes the negative fortune associated with the event.
* Unfavorable: This implies that the event will not lead to good results.
* Unfortunate: This implies that the event will bring sadness or misfortune.
* Unpropitious: This is a more formal and literary word for inauspicious.
More specific opposites depending on the context:
* Ominous: If the event is foreboding or suggests bad things to come.
* Disastrous: If the event is likely to cause significant harm or destruction.
* Unfortunate: If the event is likely to lead to sadness or misfortune.
* Unlucky: If the event is likely to bring bad luck.
The best opposite for "auspicious" will depend on the specific context in which it is used.