שום

In Yehoash's Tanakh, we came across this word (without 'keyn' and without 'on a' before it). Neither your dictionary nor Weinreich's showed the meaning.
We did find it in Harkavy's dictionary: any
Even if that meaning is now obsolete, I think your dictionary should include that meaning and show the status as obsolete.
You would likely want to add text to Section B 5.4 of your user's guide. For example: "We have included some words that are now obsolete in Yiddish because some readers may read older literature in which these words appear; such words should not be used now."

David