We could try submitting it to the Urban Dictionary.
It’s certainly debatable whether or not that is a “real” dictionary but there have been a lot of slang words and expression that I wouldn’t have understood if I hadn’t been able to look them up there.
I had a phrase accepted by them, something that came out of story @johnpowell posted, about his childhood… that I liked so much I submitted it.
And it’s the only dictionary I know of that accepts entries from just some random person, on the internet, who wants to submit a word and provide their own definition of it.
And mubbling is, as of yet, undefined. Plant your flag, @JLeslie. It’s yours, if you want it.