1. Causing fear or anxiety by threatening great harm
   "a life-threatening disease"
   - dangerous, grave, grievous, serious, severe

See also: critical

• speleology
• spell
• spell out
• spell-checker
• spellbind
• spellbinder
• spellbinding
• spellbound
• spellcheck
• spelldown
• speller
• spelling
• spelling bee
• spelling checker
• spelling contest
• spelt
• spelter
• spelunk
• spelunker
• spence
• Spencer
• Spencer Tracy
• spend
• spend a penny
• spend-all