So if OK stands for “all correct,” wouldn’t it be “AC”? Not exactly, says linguist Erin McKean, who points out that the word was intentionally misspelled. Much like the way people on the Internet shorten or abbreviate words when typing, OK was misspelled on purpose.
“For instance, a lot of kids online spell “cool,” “k-e-w-l,” says McKean, senior editor for U.S. dictionaries at Oxford Press. “They know how to spell cool, but it just looks cooler to spell it “k-e-w-l.”
It was cool in certain East Coast cities in the mid-19th century to substitute OK for “all correct.” McKean says it was common for people of that day to use inside lingo — shorthand full of puns, purposeful misspellings and abbreviations. For example, they’d use “SP” for “small potatoes,” or “TBFTB” for “too big for their britches.”