Causing fear or anxiety by threatening great harm. Synonyms:dangerous, grave, grievous, serious, severe."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"
... stoppage of breathing, and for serious bleeding. These are the two most life-threatening conditions you can do something about. They demand immediate treatment (see ... — In Time Of Emergency - A Citizen's Handbook On Nuclear Attack, Natural Disasters (1968) • Department of Defense