St. Louis Definition (regional slang term): Generally means redneck, hick, or someone from Missouri outside of St. Louis or certain areas of St. Louis.
The word itself and its most common definition have its origins in the state of Indiana (also known as the Hoosier State), though the word has taken on regional meanings outside of Indiana, most commonly in and around the St. Louis, MO area. However, even the St. Louis definition can trace its origins to Indiana and Indiana natives transplanted to the St. Louis area.
There are other definitions on Urban Dictionary that outline the St. Louis definition of the word Hoosier in some detail and the better ones include a history of the word. I won’t go through those definitions again, but I would like to point out, as I did above, that if you look at the origins of the St. Louis meaning you will see that this word, as used in St. Louis, also has its roots in Indiana.
Also, contrary to other definitions listed here, Indiana University has no mascot -- there is no “Indiana Hoosier.”
The following is from the July/August 1992 issue of the Indiana Alumni Magazine:
Still, the many theories are fascinating in their diversity. Take the one that has a contractor in 1825 named either Samuel Hoosier or Hoosher. His workers, who helped build a canal on the Ohio River, were predominantly from Indiana. They were called "Hoosier's men" or "Hoosiers."
A more colorful tale has the word deriving from the phrase fearful early settlers called out when startled by a knock on their cabin door: "Who's here?" — a call that over time degenerated into Hoosier.
And then there's the tongue-in-cheek explanation of Hoosier poet James Whitcomb Riley, who related the term to the roughness and ferocity of the state's early residents. Hoosier pioneers fought so violently, Riley contended, that noses were bitten off and eyes jabbed out during these brawls. Hoosier, said Riley, descends from the question posed by a stranger after entering a southern Indiana tavern and pushing a piece of human flesh with his boot toe: "Who's ear?"
Not nearly so clever but perhaps more plausible is the suggestion by Peckham and others that the term may derive from "hoozer" — a word that in the Cumberland dialect of Old England means "high hills."
"By extension, it was attached to a hill-dweller or highlander and came to suggest roughness and uncouthness," Peckham states. "Thus, throughout the Southeast in the eighteenth century, 'Hoosier' was used generally to describe a backwoodsman, especially an ignorant boaster, with an overtone of crudeness and even lawlessness."
That theory has won the most favor from Warren Roberts, MA'50, PhD'53, an IUB folklore professor who has shown how family surnames may have brought this form of Hoosier from Britain to its Midwest resting place.
Whatever its origin, historians agree that the nickname for Indiana residents was popularized in the 1800s by novels such as Edward Eggleston's The Hoosier School-Master, by Riley's poetry, and by newspaper articles that used it. As a result, although its historical roots may never be discovered, Hoosier is perhaps the most widely recognized state nickname. But even this modern meaning is ambiguous, and the word's use ranges from complimentary to derisive, depending on who is using it.
St. Louis Example: Did you see the gun-rack in Craig's pick-up? He's such a hoosier.