ominous

Adjective

• presaging ill fortune
  • ill omens
    
  • ill predictions
    
  • my words with inauspicious thunderings shook heaven- P.B.Shelley
    
  • a dead and ominous silence prevailed
    
  • a by-election at a time highly unpropitious for the Government
    

• threatening or foreshadowing evil or tragic developments
  • a baleful look
    
  • forbidding thunderclouds
    
  • his tone became menacing
    
  • ominous rumblings of discontent
    
  • sinister storm clouds
    
  • a sinister smile
    
  • his threatening behavior
    
  • ugly black clouds
    
  • the situation became ugly
    

Related words

• Synonyms: 
  ill , inauspicious , baleful , forbidding , menacing , minacious , minatory , sinister , threatening