From WordNet (r) 2.0 (August 2003) [wn]:
life-threatening
adj : causing fear or anxiety by threatening great harm; "a
dangerous operation"; "a grave situation"; "a grave
illness"; "grievous bodily harm"; "a serious wound"; "a
serious turn of events"; "a severe case of pneumonia";
"a life-threatening disease" [syn: dangerous,
grave, grievous, serious, severe]