This could put the kibosh on our plan, my friend Paul wrote during an instant message conversation. I had never come across this expression and kibosh reminded me of shibboleth, so I immediately assumed it was of Jewish origin. Wrong!
836, kye-bosk, in slang phrase “put the kibosh on”, of unknown origin, despite intense speculation. Looks Yiddish, but origin in early 19c. English slang seems to argue against this. One candidate is Ir. 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”].
The French translation could be: Cela pourrait mettre notre plan en l’air.