- know-nothing
- know one's business
- know one's onions
- know one's stuff
- knows
- knows one's stuff
- know stuff
- knows what's what
- know the answers
- know the ins and outs
- know the ropes
- know the score
- know what's what
- know what makes someone tick
- knuckle
- knuckleballer
- knuckle down
- knuckle down to
- knuckle-dusters
- knucklehead
- knuckles
- knuckle sandwich
- knuckle to
- knuckleunder
- knuckle under
- knuckle with
- knuckling under
- knucks
- knurl
- knurled
- knurly
- KO
- koala
- kobold
- Kodachrome
- Kodak
- kolkhoz
- Konzentrationslager
- kook
- kooky
- kosher
- kosher dill pickle
- kowtow
- kowtower
- kowtowing
- KP
- kraken
- krater
- K ration
- Krebs cycle
- kriegspiel
- kris
- Kriss Kringle
- kudize
- kudo
- kudos
- kung fu
- kvetch
- kvetching
- kyphosis
- kyphotic
