1. Vitally important
   - life-and-death

See also: crucial, important

• Kleist
• Klemens Metternich
• kleptocracy
• kleptomania
• kleptomaniac
• klezmer
• klick
• klieg light
• Klimt
• Kline
• Klinefelter
• Klinefelter syndrome
• Klinefelter's syndrome
• klipspringer
• klondike
• kloof
• Klopstock
• Klorvess
• Klotho
• kludge
• klutz
• klutzy
• Kluxer
• klystron
• Klyuchevskaya