After at least 138 years of discussion, the etymological puzzle is possibly solved: the originally British English informalism kibosh as in “put the kibosh on [something]” could come from the clogmakers’ term kybosh ‘iron bar which, when hot, is used to soften and smooth leather’ (with possible reinforcement from Western Ashkenazic British English khay bash ‘eighteen pence’)

Abstract

The sources suggested for the originally British and variously spelled English slang idiom put the kibosh on [...] are so diverse — ranging, for example, from Irish and Scots Gaelic to Yiddish and Hebrew, not to mention English — that no one person could possess enough knowledge to evaluate all of them competently and to answer all the questions that must be answered before we could say “case closed”. For that reason, the author of the present article treads here, as his wont is, only where he feels sure of foot.