As the new year begins, we’re reeling from an overload of retrospective lists: top news stories; persons of the year; scandals of the year (and their subsets: financial scandals of the year, celebrity scandals of the year, etc.); viral videos of the year, ad nauseam. (Yes, that’s how it’s spelled, no matter how many times you’ve seen it as “ad nauseum.”)

One list that has surged in recent years is “words of the year.” (“Surge” was a finalist for the American Dialect Society’s 2006 “word of the year.”) Of course, there’s not just one list. Every dictionary, linguist, or word society seems to have its own—at least each one attached to a public relations agency or Twitter account.

This year, for example, The New Oxford American Dictionary, which looks at words in use, chose “unfriend” as its “word of the year.” Among its runners-up were “hashtag” (the symbol # used to “tag” a subject or continuing conversation on Twitter), “death panel,” and “sexting,” sending suggestive texts or pictures via cellphone. Merriam-Webster, which rates words by how much they were looked up in its online dictionaries, lists “admonish” as its “word of the year,” followed by “emaciated,” “empathy,” and “furlough.”Webster’s New World, which also picks based on usage, chose “distracted driving.” Among the runners-up were “cloud computing,” “netbook,” and “wrap rage,” anger at being unable to open a plastic or cardboard package.

The lists can be faddish. Remember “overshare”? Didn’t think so. That was WNW’s 2008 word of the year, and it means “sharing too much information” (also known as “TMI”). Its finalists were “leisure sickness,” “cyberchondriac,” “selective ignorance,” and “youthanasia.” Go ahead. Use them in a sentence.

But then there’s “locavore.” That was NOAD’s word of 2008, and it’s now in many dictionaries. And “blog,” which the ADS named as the 2002 word “most likely to succeed.” It certainly did. Other ADS “word of the year” candidates for 2002 included “Amber alert,” “regime change,” “google” as a verb, and the winner, “weapons of mass destruction,” all of which are now widely used and (mostly) accepted. (The selection of the 2009 ADS “words of the year” is Jan. 8.)

Many of these words are manufactured, in the sense that someone, somewhere, just came up with something—what, for example, prompted the invention of a “youthanasia,” a word to describe having way too many cosmetic alterations? Others are “repurposed” words, the way the trademark noun “Google” became a verb. (Though Google officially bans using its trademark as a verb, its lawyers are less quick to admonish than those of, say, Xerox.) Others are conflations, words created by mushing other words together and sometimes abbreviating them, as in “blog” (short for “Web log.”). Still others are alternate spellings of existing words, as in “phishing,” voted by the ADS as 2004’s word “most likely to succeed.”

The point is not to praise or condemn, but to help illuminate how fickle language is. The problem, of course, is knowing when a word or phrase has caught on enough for use in general-interest publications. That’s a much trickier proposition than merely listing what others have determined to be “words of the year.” If you know who is in your audience, you’ll know what words they use regularly or understand, and which ones have been “plutoed.”*

*”Plutoed” was the ADS “word of the year” for 2006, and means “demoted or devalued,” the way Pluto was when it lost its planetary status. Yeah, that one caught on.

Merrill Perlman managed copy desks across the newsroom at The New York Times, where she worked for 25 years.