adjective, noun Slang.
Examples from the Web for mostest
“I was a waiter and she was the hostess with the mostest,” said Berman.
Pappy plants cotton and mostest de time he raises better'n half de bale to he acre.
The art of war has been defined as getting the mostest men there the fustest.
When butchering time come, us stewed out the mostest lard and we had enough side-meat to supply the plantation the year round.Slave Narratives: a Folk History of Slavery in the United States From Interviews with Former Slaves|Work Projects Administration
The art of railroading comes to mean moving the mostest trains the soonest.
He say us can stay and work de land on shares, but mostest left.