kibosh n.

1836, kye-bosk, in British English slang phrase put the kibosh on, of unknown origin, despite intense speculation. The earliest citation is in Dickens. Looks Yiddish, but its original appearance in a piece set in the heavily Irish "Seven Dials" neighborhood in the West End of London 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 this is identified as a gruesome method of execution "employed by Brit. forces against 1798 insurgents" [Bernard Share, "Slanguage, A Dictionary of Irish Slang"]. Coles' dictionary of "difficult terms" (1684) has cabos'd "having the head cut off close to the shoulders." Or the word might somehow be connected with Turkish bosh (see bosh).