Why was clemency trending last week?
1836, kye-bosk, in slang phrase put the kibosh on, of unknown origin, despite intense speculation. The earliest citation is in Dickens. Looks Yiddish, but origin in early 19c. English slang seems to argue against this. One candidate is Irish caip bháis, caipín báis "cap of death," sometimes said to be the black cap a judge would don when pronouncing a death sentence, but in other sources identified as a gruesome method of execution "employed by Brit. forces against 1798 insurgents" [Bernard Share, "Slanguage, A Dictionary of Irish Slang"]. Or it may somehow be connected with Turkish bosh (see bosh).
To quash or stifle; put the quietus to: I was praying that the kid wouldn't put the ''kibosh'' on me
[1836+; origin unknown and richly speculated upon; many regard it as probably fr Yiddish because it sounds as if it ought to be; Padraic Colum, however, attributed it to Irish cie bais, ''cap of death,'' presumably the black cap donned by a judge before pronouncing the death sentence, which is a semantically appealing suggestion; the phrase was used by Dickens in his first published book, in 1836, and put into the mouth of a London urchin]