calamitous

Adjective

• (of events) having extremely unfortunate or dire consequences; bringing ruin
  • the stock market crashed on Black Friday
    
  • a calamitous defeat
    
  • the battle was a disastrous end to a disastrous campaign
    
  • such doctrines, if true, would be absolutely fatal to my theory- Charles Darwin
    
  • it is fatal to enter any war without the will to win it- Douglas MacArthur
    
  • a fateful error
    

Related words

• Synonyms: 
  black , disastrous , fatal , fateful