mostest

pronoun

most·​est ˈmō-stəst 

nonstandard, often humorous

—used in place of most (as in imitation of childlike speech)

… Americans are such suckers for TV commercials that we are powerless to resist the product that hits us with the mostest.

—Russell Baker

The disposition of personal property often becomes a scavenger hunt. Items are tagged while last breaths are being gasped. To the crudest goes the mostest.

—Thomas Easton

Lady Pamela Berry, wife of a newspaper proprietor and in her day the London hostess with the mostest, had given a dinner party in May 1951 that deserves both literary and historical footnotes.

—Geoffrey Wheatcroft

Word History

First Known Use

1833, in the meaning defined above