Confusion Abounds On Biannual, Biennial, Semiannual

business meeting If you attend an event that is held twice a year, is it a biannual, semiannual, or biennial event?

What if it is held every other year? Is it a biannual, semiannual, or biennial event?

The prefix bi means two or twice, double: bifocal, bipolar, bilingual, bipartisan

The prefix semi means half or part, less than fully: semicircle, semifinal, semiconscious, semiprivate

Here’s the problem:

When the prefix bi is used with terms that designate time, is it “twice each” or “every two”?

The same is true with semi; does it mean, for example, twice a year or every two years?

According to my primary source, The Associated Press Stylebook:

  • biannual means twice a year
  • biennial means every two years
  • semiannual means twice a year

Here are other sources and their definitions:

grammarist.com
biannual means occurring twice a year
biennial can mean occurring every two years or every other year
semiannual means occurring twice a year

onlinegrammar.com
biannual means twice a year
biennial means lasting or recurring every two years
semiannual not addressed, but bimonthly means every two months and twice a month

grammarbook.com
biannual means twice a year
biennial means occurring every two years
semiannual means twice a year

The Careful Writer by Theodore M. Bernstein
biannual means twice a year
biennial means every two years
for semi, he says: refer to bi (Which bi: twice each or every two?)

With regard to bimonthly, Bernstein writes: “It means every two months, and nothing else.” He claims that biweekly means every two weeks, but adds, “It sometimes can mean twice a week.”

Huh?

Do we have a consensus?

  • Biannual seems to consistently mean twice a year.
  • Biennial can mean every two years (i.e. every other year) or lasting two years.
  • Semiannual means twice a year, so it is interchangeable with biannual.

The confusion about prefixes bi and semi are aspects of English that make me crazy. It’s not difficult to recognize that bi means two, but bi can mean different things when combined with different elements of time.

This Ruthless Editor will avoid bi words and semi words in writing and speaking about time. Out of consideration for readers and in the interest of clarity, I will simply write twice a year (or week or month), or every other year (or week or month), or lasting for two years.

Have you been confused about biannual, biennial and semiannual or other forms of words with the suffixes bi and semi? Please let me know if you’ve found other solutions.

Kathy Watson
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Kathy Watson

Kathy has a love/hate relationship with grammar; she loves words and the punctuation that helps them make sense, yet she hates those pesky rules. A self-proclaimed ruthless editor, she prefers standard usage guidelines of The Associated Press Stylebook. Her easy-to-use Grammar for People Who Hate Rules helps people write and speak with authority and confidence. She encourages and welcomes questions and comments. (Email)

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4 thoughts on “Confusion Abounds On Biannual, Biennial, Semiannual

  1. morst

    You are a language detective! Another excellent post!

    Frustrating that there is no consensus, but fascinating that we can get along without one! 😉

    1. Kathy WatsonKathy Watson Post author

      morst: Yes, with such variety in word use and so many choices, it is remarkable that we manage to successfully communicate. Appreciate your comment.

  2. C Van Domelen

    I prefer you solution. I used to tell my students that If they had any doubt about a word or phrase, they should find an alternative word or expression.
    P.S. I am always nervous when I comment here. ^_^

    1. Kathy WatsonKathy Watson Post author

      I agree: When there seems to be no solution, rewriting can save the day. Thanks for overcoming your apprehension about commenting. I truly appreciate your feedback!

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