Synonyms of the word

life-or-death

• adj. Of critical importance to the survival of a living organism.
• adj. Having death as a possible or even likely outcome; perilous.
• adj. Of critical importance to the success of a particular endeavor.

crucial

• adj. Being essential or decisive for determining the outcome or future of something; extremely important.
• adj. (archaic) Cruciform or cruciate; cross-shaped.
• adj. (slang, chiefly Jamaica) Term of approval, particularly when applied to reggae music.

important

• adj. Having relevant and crucial value.