Dictionary:

catastrophic

  (kăt'ə-strŏf'ĭk)

1. Of, relating to, or involving a catastrophe.
2. Involving or resulting in substantial, often ruinous medical expense: a catastrophic illness.

adjective

Causing ruin or destruction: calamitous, cataclysmal, cataclysmic, destructive, disastrous, fatal, fateful, ruinous. See help/harm/harmless.

Definition: disastrous
Antonyms: beneficial, fortunate

The adjective has one meaning:

Meaning #1: extremely harmful; bringing physical or financial ruin
  Synonym: ruinous