kibosh

The etymology of "kibosh" is famously obscure and debated, adding to its intriguing character. The most compelling theory traces it to the Irish Gaelic phrase caidhp bháis, literally "cap of death," which was the black cap a judge would don before pronouncing a capital sentence, thus figuratively bringing matters to a final, fatal conclusion. Another plausible candidate is the Yiddish word kabát, meaning "a long coat," which entered English slang via the tailoring trade; the idea of "putting the kibosh on" something may have evolved from the notion of putting a final, finishing coat on a garment. Regardless of its precise origin, the word entered London slang in the early 19th century and solidified its modern meaning of bringing something to an abrupt and definitive end.

The word is considered an unsegmentable simplex. Its origin is uncertain, with proposed links to Irish caidhp bháis (meaning "cap of death," referring to a black cap worn by a judge pronouncing a death sentence) or Yiddish kabát (a coat, possibly via the phrase "to put the kibosh on" meaning to finish off, as in a final coat of paint). Its functional role is as a complete lexical unit.