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

See also: critical

• Fundulus majalis
• fundus
• fundy
• funeral
• funeral chapel
• funeral church
• funeral director
• funeral home
• funeral march
• funeral parlor
• funeral parlour
• funeral pyre
• funeral undertaker
• funeral-residence
• funerary
• funereal
• funereally
• funfair
• fungal
• fungal infection
• Fungi
• Fungi imperfecti
• Fungia
• fungibility
• fungible