- Klaipeda
- Klamath
- Klamath Falls
- Klamath River
- klammath weed
- Klan
- Klansman
- Klaproth
- Klaus Fuchs
- klavern
- Klavier
- klaxon
- Klebs-Loeffler bacillus
- klebsiella
- Klee
- Kleenex
- Klein
- Klein bottle
- Kleist
- Klemens Metternich
- kleptomania
- kleptomaniac
- klick
- klieg light
- Klimt
- Kline
- Klinefelter
- Klinefelter syndrome
- Klinefelters syndrome
- Klondike
- Klopstock
- Klorvess
- Klotho
- kludge
- klutz
- Kluxer
- klystron
- Klyuchevskaya