Flus, gnus, emus, and tutus

Flu season is upon us. The word flu is typically a mass noun, meaning it isn't often used in the plural. But, like all mass nouns, it can be, because there are many different kinds of flu. This raises the question: how do you spell the plural of flu?

If you found the word flus by itself written on a piece of paper, it would look very odd: "What the heck's a FLUSS??" you might wonder. Thus, you might be tempted to do something else with the plural, such as adding an e before the s. However, this would give you flues, which is the plural of a different word designating part of a chimney. Or you might think about sticking in an apostrophe, "flu's", but this is not recommended.

Bear in mind that words are almost never devoid of context that [fancy lexicographer word alert] disambiguates them. You probably did stumble over the title of this post, because of the lack of semantic context to help you. But if you are talking about flu in the plural, it is likely to be in a phrase like "colds and flus" or "there are a lot of different flus going around this year", so your readers shouldn't stumble, or at least not for long. There aren't many words in English ending in -u, but those that do exist (e.g. gnu, emu, tutu) all form their plural by simply adding an s. By the way, if you want to see some really funky tutus, visit this post.

You can, of course, also avoid the problem by sticking to using flu as a mass noun: "Colds and flu are taking a toll this year."

The word flu was a 19th-century shortening of “influenza”, which the English had borrowed from Italian in 1743. Influenza, like the English word “influence”, comes from the Latin influere (to flow in).In the Middle Ages, astrologers believed that an ethereal fluid flowing from the stars or heavens affected people's characters and events generally, so influenza in Italian and “influence” in English referred to the impact of the stars on human life. Since this kind of influence was thought also to cause illness, Italians used influenza to mean a “visitation” of an epidemic disease, an influenza of chicken pox, catarrh, and so on. When a particularly nasty flu outbreak hit Italy in 1743, people just used the word la influenza by itself. As flu does, it spread, and the English adopted the Italian name.

As for the part of a chimney, the flue, its origin is unknown.