Fatal (adjective)

1. Causing or resulting in death.
2. Having a disastrous or detrimental effect.

Origin:

Late middle english: from latin fatalis, from fatum "fate".

Examples:

1. The crash was fatal and killed several people.
2. The mistake was fatal to the company's success.
3. The disease was fatal and had no cure.
4. The exposure to the toxic gas was fatal.
5. The error in judgement was fatal.