life-or-death

adjective3

1. •
   Of critical importance to the survival of a living organism.

   • Good camoflouge is life or death for many animals in the wild.
2. •
   Of critical importance to the success of a particular endeavor.

   • Obtaining financing was a life-or-death matter for the research.
3. •
   Having death as a possible or even likely outcome; perilous.

   • Ascending Mount Everest can be life or death for an inexperienced climber.