I was watching American Primeval (on Netflix), when the boy said “okay,” and I thought, that sounds anachronistic. Then I thought, wait, “okay” was a fad from the 1800s that stuck; let’s look into this.
The show is set in 1857, around the Utah Territory. The boy has traveled west from Philadelphia.
The origin of OK is disputed:
Most modern reference works hold that it originated around Boston as part of a fad in the late 1830s of abbreviating misspellings; that it is an initialism of “oll korrect” as a misspelling of “all correct”. This origin was first described by linguist Allen Walker Read in the 1960s.
[…]
Read argues that, at the time of the expression’s first appearance in print, a broader fad existed in the United States of “comical misspellings” and of forming and employing acronyms, themselves based on colloquial speech patterns:
The abbreviation fad began in Boston in the summer of 1838 … and used expressions like OFM, “our first men,” NG, “no go,” GT, “gone to Texas,” and SP, “small potatoes.” Many of the abbreviated expressions were exaggerated misspellings, a stock in trade of the humorists of the day. One predecessor of OK was OW, “oll wright.”
The general fad is speculated to have existed in spoken or informal written U.S. English for a decade or more before its appearance in newspapers. OK’s original presentation as “all correct” was later varied with spellings such as “Oll Korrect” or even “Ole Kurreck”.
The term appears to have achieved national prominence in 1840, when supporters of the Democratic political party claimed during the 1840 United States presidential election that it stood for “Old Kinderhook”, a nickname for the Democratic president and candidate for reelection, Martin Van Buren, a native of Kinderhook, New York. “Vote for OK” was snappier than using his Dutch name.[11] In response, Whig opponents attributed OK, in the sense of “Oll Korrect”, to the bad spelling of Andrew Jackson, Van Buren’s predecessor. The country-wide publicity surrounding the election appears to have been a critical event in OK’s history, widely and suddenly popularizing it across the United States.
[…]
In “All Mixed Up”, the folk singer Pete Seeger sang that OK was of Choctaw origin, as the dictionaries of the time tended to agree. Three major American reference works (Webster’s, New Century, Funk & Wagnalls) cited this etymology as the probable origin until as late as 1961.
The earliest written evidence for the Choctaw origin is provided in work by the Christian missionaries Cyrus Byington and Alfred Wright in 1825. These missionaries ended many sentences in their translation of the Bible with the particle “okeh”, meaning “it is so”, which was listed as an alternative spelling in the 1913 Webster’s.
Byington’s Dictionary of the Choctaw Language confirms the ubiquity of the “okeh” particle, and his Grammar of the Choctaw Language calls the particle -keh an “affirmative contradistinctive”, with the “distinctive” o- prefix.
“Och aye” Scotch okay.
I go for the Choctaw hypothesis. Languages borrow words from each other. In English English it is common to say, “Do you follow me,” meaning “Do you understand me.” This came from Wellington’s Peninsular Wars of the first decade of the 1800s. The Portuguese word falo means to speak and the English troops would have asked the locals, “Do you falo English?”