käft

From Old Swedish kiæpter, from Old Norse kjaptr. Cognate with Danish kæft, Norwegian kjeft, Icelandic kjaftur, and Faroese kjaftur.

käft c

1. a jaw or (open) mouth of an animal (especially one with a powerful bite)

   Synonym: (jaw of a human or animal) käke

   hajens käftar

   the jaws of the shark

   Hunden hade ett ben i käften

   The dog had a bone in its mouth

3. (colloquial, mildly offensive) a mouth of a human

   Synonym: mun (“mouth”)

   slå någon på käften

   punch someone in the face (or "mouth," literally – aggressive-sounding)

   slänga käft

   talk (literally "throw jaw")

   vara slängd i käften

   be quick to answer, have the gift of gab (literally "be thrown in the jaw")

   att låta käften gå

   to keep talking

4. (colloquial, in the expression "inte en käft") a person

   Synonyms: kotte, jävel

   Jag kom till kontoret kl. 8 och det var inte en käft där

   I came to the office at 8 o'clock and not a soul was there

(sense 2) conjures the image of animal jaws, giving it a colloquial and mildly offensive (or jocular) feeling. This plays into making håll käften very rude, as it's telling someone to keep their animalistic jaws shut.

• munläder

käft

1. shut up (short for håll käften)

   Synonym: käften

Can take on a jocular tone, which is rare for the harsher håll käften.

• käft in Svensk ordbok (SO)
• käft in Svenska Akademiens ordlista (SAOL)
• käft in Svenska Akademiens ordbok (SAOB)
• käft in Elof Hellquist, Svensk etymologisk ordbok (1st ed., 1922)