I also liked the definition which suggested
that "whister"
came from "wheesht,"
as in "hauld yer wheesht!"

So, a blow to the ear -- back-handed, in some dictionaries --
saying "hauld yer wheesht," or "shut yer yap," in non-verbal terms.

The "clister" is just there to rhyme with "whister"?
One version pointed out that "clyster" means enema -- huh??