calamitous (adj.)

• afflictive
• awful
• baneful
• black
• cataclysmal
• cataclysmic
• catastrophic
• consuming
• consumptive
• deadly
• destroying
• destructive
• devastating
• dire
• disastrous
• distressful
• distressing
• dreadful
• fatal
• fateful
• grievous
• heartbreaking
• internecine
• lamentable
• nihilistic
• pernicious
• ravaging
• regrettable
• ruinous
• self-destructive
• subversive
• suicidal
• terrible
• tragic
• unfortunate
• wasteful
• withering
• woeful