Learn English – Where did the term “fickle mistress” come from

According to the OED, the term OK began its days as a humorous initialism “apparently derived from the initial letters of oll (or orl) korrect, jocular alteration of ‘all correct’ ”, when it was first seen almost 200 years ago in the United States, way back in 1839.

It seems that this sort of off-kilter formation was considered quite funny at the time: “an instance of a contemporary vogue for humorous abbreviations of this type” per the OED.

By 1840, this use was “greatly reinforced by association” with another identical initialism O.K., this one derived from the nickname Old Kinderhook adopted by Martin Van Buren during his 1835 electoral campaign for the U.S. presidency. The corresponding verb was soon null-derived¹ from this initialism around 1882.

The OED further notes (with bold emphasis added in this post for clarity) that:

Other suggestions, e.g. that O.K. represents an alleged Choctaw word oke ‘it is’ (actually the affirmative verbal suffix -okii ‘indeed, contrary to your supposition’), or French au quai, or Scottish English och aye, or that it derives from a word in the West African language Wolof via slaves in the southern States of America, all lack any form of acceptable documentation.

The OED further states that “Competing theories as to the origin of the expression have been in evidence almost since its first appearance”, and then provides several early completing theories in support of that assertion.

Footnotes

1. Null derivation, also known as zero derivation, is when a word is conscripted unchanged into use for a part of speech that’s different from the customary one. It has no derivational affix and so is said to be null derived, such as when we null-derive nouns from adjectives in The Good, the Bad, and The Ugly. A clearer example of this is the classic refrain that “verbing weirds language”, which features two instances of null-derivation: not only does it null-derive a new verb “verb” from its noun and then uses its verbal -ing inflection as a subject, it also null0derives a new verb “weird” from its adjectives and then uses the new verb’s third-person singular inflection.

Interestingly enough, Etymonline suggests that it has nothing to do with cheese:

"cheap, inferior," 1896, from Urdu chiz "a thing," from Persian chiz, from O.Pers. *ciš-ciy "something," from PIE pronomial stem *kwo- (see who). Picked up by British in India by 1818 and used in the sense of "a big thing" (especially in the phrase the real chiz). By 1858, cheesy had evolved a slang meaning of "showy," which led to the modern, ironic sense.

Cheese, on the other hand, ultimately comes from Latin (caseus), taking a detour via West Germanic (compare German Käse, Dutch kaas).