life-threatening
adjective
life-threat·en·ing ˈlīf-ˌthret-niŋ 
-ˌthre-tᵊn-iŋ
: capable of causing death : potentially fatal
a life-threatening disease/condition
The injuries are serious but not life-threatening.
Word History
First Known Use
1759, in the meaning defined above
Medical Definition
life-threatening
adjective
life-threat·en·ing ˈlīf-ˌthret-ən-iŋ
: capable of causing death : potentially fatal
life-threatening injuries
a life-threatening allergic reaction
life-threatening arrhythmia