Here’s how language changes:

Take a term rendered in a foreign language, let’s say “yin and yang.” Have people start mispronouncing (and misspelling) it as “ying and yang,” bring in a slang term for what polite people call the buttocks—“she’s got talent out the ying-yang,” add a rap group called the Ying-Yang Twins, and pretty soon more people will think that “ying” is correct.

It’s an easy mistake to make. “Yin and yang,” after all, is the complement of opposites: Yin, the feminine, is dark, passive, and negative, while yang, the masculine, is light, active, and positive. The symbol——is complementary, too. So why shouldn’t the words be complementary, differing by only one letter? Except that they’re not.

The mistake is so common that even the online version of Webster’s Third New International Dictionary, Unabridged makes it in its entry for “yin-yang.” After defining the term as “being or comprising opposite and especially complementary elements,” Webster’s cites Diane McWhorter’s mention of the “ying-yang system of good and evil”—even though McWhorter spelled it correctly in the book review the dictionary is citing.

So it’s no surprise that, hundreds of times a year, news organizations refer to “the ying and yang” of a situation. (Occasionally, there’s a “ying and yan,” but those are much less prevalent.) In addition to “ying-yang,” another variant is “yingyang.”

Most of the time it’s a simple typo, but if you look at user-generated dictionaries like urbandictionary.com or onlineslangdictionary.com, enough people believe that is the correct spelling that it may someday be acceptable. So far, though, the alternative spelling—or the slang—doesn’t seem to have made it into any of the major dictionaries or usage guides, except as a typo.

Not so “wazoo,” another reference to one’s posterior. As with “ying-yang,” the phrase “out the wazoo” means an abundance. One can also claim that something is a “pain in the wazoo,” and even people who don’t know what a “wazoo” is will understand.

Here, the venerable Oxford English Dictionary weighs in. While it professes not to know the origin of “wazoo,” it says that others suspect it may come from the French oiseau, or bird, through a Louisiana Creole term, “razoo,” for raspberry. (Those with particularly fertile dirty minds may be able to make the connection.) It’s almost exclusively American.

The OED’s first two citations are telling in themselves. The first, in 1961, is from a University of California, Berkeley publication: “Run it up yer ol’ wazoo!” Its second citation is from a publication not known for its use of slang, The Wall Street Journal, in 1971: “Golf itself is quite safe, the greatest risk being the possibility of a long drive plunking some poor fellow in the wazoo.”

If you want to be “correct,” use “yin and yang” when you’re referring to the light-dark contrasts. Use the slang “ying-yang” or “wazoo” as you see fit, but don’t be surprised if a proper schoolmarmish person tells you to blow it out your ear.

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Merrill Perlman managed copy desks across the newsroom at The New York Times, where she worked for 25 years. Follow her on Twitter at @meperl.