1. Vitally important
   "a life-and-death struggle"
   - life-or-death

See also: crucial, important

• Usnea
• Usnea barbata
• Usneaceae
• Usonian
• USP
• USPS
• usquebaugh
• USS
• USS Cole
• Ussher
• USSR
• USSS
• Ustilaginaceae
• Ustilaginales
• Ustilaginoidea
• Ustilaginoidea virens
• Ustilago
• Ustilago maydis
• Ustinov
• usual
• usually
• usualness
• usufruct
• usufructuary
• Usuli