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Grammar 101: Biannual, Semiannual, Biennial

March 30th, 2009 by
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Calendar - Biannual, Semiannual, or Biennial?

One of the most important reasons why you need good grammar is for the sake of clarity. When your language is imprecise, the meaning of your words can turn out to be quite ambiguous. You need to use the right words at the right time. This way, your readers and your listeners can know exactly what you are trying to say.

Just as you don’t want to confuse complement with compliment or less with fewer, you also want to be very clear when it comes to describing the frequency of events. Do you ever confuse biannual with biennial? It’s a common error, considering the root of these words and how similar they sound. Let’s have a look at the difference.

Let’s start with semiannual. If you break this word down into its two main parts, it’s fairly easy to discern its meaning. Semi- denotes the “half” of something. When you talk about a semicircle, you are talking about half a circle (180-degrees). Annual denotes that this word has something to do with a year. This is the same root that gives us the word anniversary. In this way, semiannual (or semi-annual, if you prefer) indicates that an event is taking place every half a year. In other words, a semi-annual sale would take place every six months (twice a year).

Where there can be a great deal of confusion is with the word biannual. Breaking this word into its two main parts can actually make the matter even more confusing. The annual part of the word remains the same as in semiannual, but the bi- portion suggests that the number two is involved. For instance, a bicycle has two wheels. The supposedly bipartisan politics of Barack Obama address both major political parties. Given these meanings, you may be inclined to believe that a biannual event takes place every two years. And you’d be wrong. A biannual event actually takes place twice a year, just like a semiannual event.

How, then, do you denote an event that takes place every two years? That’s where the term biennial comes into play. If you get your eyes tested by your optometrist every two years, you go for biennial checkups.

Probably one of the best ways to avoid further confusion in the future is to minimize your use of the word biannual, as that’s the word that seemingly (and incorrectly) straddles between the meanings of “every six months” and “every two years.” Stick to using semiannual and biennial, and your meaning should be clearer.

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Michael Kwan Freelance Writer

9 Responses to “Grammar 101: Biannual, Semiannual, Biennial”

  1. Nick says:

    Yeah, I most definitely have used biannual to mean every two years and thought that was correct. Guess I’ll have to be more careful in the future. Maybe I’ll take the easy way out and just say every two years instead of remembering to use biennial…instead of a biennial event I could say the even that happens every two years :)

  2. Zagorath says:

    Wow thanks! This is a really useful post. I never knew that. A always thought that biannual could be used for both meanings.
    I do intend to try and use biennial and semiannual from now on. Or; as Nick said before me; just say the event happens every two years, or twice a year.

  3. Joe says:

    Does the same “bi” definition apply to other time periods? For example, mortgage companies try to sell restructured programs that include “biweekly” payments (every other week or two per month). And I have seen “bimonthly” magazine subscriptions (every other month or six issues per year). Are these correct uses of “bi”?

    • Michael Kwan says:

      As I understand it, yes. In the strictest sense, though, paying every other week or paying twice a month are not the same thing. The former has 26 payments in a year and the latter has 24. Every other week would be biweekly, whereas twice a month would be semi-monthly.

  4. Tim says:

    Although I agree with your conclusion, the definition of biannual includes (unfortunately) both meanings. The same confusion exists for bimonthly and biweekly. One dictionary I have has a usage section that says something to the effect of “the dictionary won’t help” adding that the confusion is perpetuated in part because everyone thinks their understanding is right without question.

    I personally have always used semiannual for twice a year and the less common usage of biannual for every other year. I was one who thought myself correct! It took a crossword puzzle to enlighten me. :-)

    • Xenobio says:

      Yes, either one is “correct” from a historical usage and dictionary definition point of view – but obviously this leads to massive confusion. So if anybody is thinking of using this in a professional context like business or science, I would REALLY encourage using explicit numbers like “every 6 months” and “every 24 months” instead of “biannual”/”biennial”. In the worst-case scenario, getting the two mixed up could result in getting your organization shut down if something critical is done a year and a half late!

      There are times and places for using elegant, slightly archaic words and there are times and places for being as explicit as possible even if it doesn’t sound nice. Business and science communications are definitely the latter.

      The only time I’ve seen “biennial” used in the wild is in the context of several different art shows that are called the “Biennale” – Singapore for instance has one.

  5. Eloise says:

    I beg to differ. While semiannual does mean every 6 months for the reasons you stated, biannual simply means twice a year. That doesn’t automatically make a biannual even occurring every 6 months. So:
    A semiannual event might take place in January and July; but a biannual event could take place in January and September.

  6. Eloise says:

    typo …. “event”, not “even”.

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