Definitions:

1. Implies that the outcome of the event or action will likely be unpleasant or harmful. ADVERB
   • The door creaked open ominously, as is someone- or something- was waiting inside.
2. In an ominous manner. ADVERB
   • The sun darkened ominously.
3. Refers to actions, words, or situations that suggest something bad or threatening may occur. ADVERB
   • The sky darkened ominously before the storm hit.
4. Used to describe situations, sounds, or signs that create a feeling of impending danger or doom. ADVERB
   • He spoke ominously, warning them not to go any further.

Synonyms:

• bleak
• dangerously
• darkly
• forebodingly
• grimly
• menacing
• sinister
• threateningly