Two-word expressions often cause trouble when they are combined with yet a third word, becoming compound modifiers. Most journalists have heard of the “small businessman” who is supposed to become the “small-business man” to avoid having readers think, even for a second, that the businessman is height-challenged.

Many style guides, even those that try to avoid hyphens, recommend putting that hyphen in, using the same logic as The Associated Press: “The principle of using a hyphen to avoid confusion explains why no hyphen is required with very and -ly words. Readers can expect them to modify the word that follows. But if a combination such as little-known man were not hyphenated, the reader could logically be expecting little to be followed by a noun, as in little man. Instead, the reader encountering little known would have to back up mentally and make the compound connection on his own.”

Not a lot of people have trouble with those constructions, probably because “small” and “little” are adjectives, and everyone knows adjectives modify nouns. Instead, the trouble comes when both modifiers are words that are usually nouns, as in “health care policies.” Do you put in a hyphen, or don’t you? Is “health” modifying “care” or “policies” or both? Maybe two hyphens are needed? (Never!)

Perhaps because of that confusion, in recent years there’s been a tendency to avoid the issue entirely by making the two modifying nouns into a single noun: “healthcare.” In the past month alone, “healthcare” has appeared more than a thousand times in mainstream news, wire, and magazine reports, as a stand-alone noun and as an adjective, helped along by companies that have adopted “healthcare” in their names. Most appearances are in publications that do not follow AP style, which still wants “health care” to be two words.

Webster’s New World College Dictionary , often the slowest to adopt word changes, seems to prefer “healthcare” as a one-word noun, adding, “also written health care.” So does the New Oxford American Dictionary, but, somewhat surprisingly, Merriam-Webster and American Heritage do not, despite their forward-looking reputations. (Of course, it should be noted that Webster’s also allows such odd compounds as “airstrike” and “firetruck.”)

It’s inevitable that “healthcare” will eventually become one word everywhere. The same is happening with “day care,” which is already rendered as “daycare” in American Heritage (“day care” is called a “variant” spelling), though not in the other dictionaries mentioned here. Let’s hope, though, that it doesn’t spread too far, or we’ll end up with monstrosities like “incometax” or “hamburgerbun.”

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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.