Biannual vs. biennial: what's the difference?

Biannual vs. Biennial: What’s the Difference?

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I’m back with more easily confused words. Biannual and biennial are both homophones, which means they sound similar but have different meanings. It’s also worth noting that there’s a third option that some people may also find confusing—semiannual!

In this blog post, I will take a closer look at these words and their differences and provide you with examples of how to use them correctly.

Quick Definitions of Biannual, Biennial, and Semiannual

Biennial: occurring every two years or lasting for two years.

Biannual: occurring twice a year or half-yearly.

Semiannual: occurring twice a year or every six months.

When to Use Biannual

Biannual is an adjective that means twice a year.

The adverb form is biannually. When something happens biannually, it happens twice a year.

Bi- is a prefix that means two, twice, doubly, or occurring every two.

Examples of Biannual in a Sentence

  • Join us for our biannual fundraising ball; we missed you at the last one earlier this year.
  • The biannual conference will be held in Brazil in January and Austria in July.

When to Use Biennial

Biennial is an adjective that means occurring every two years or continuing or lasting for two years.

The adverb form is biennially. If something happens biennially, it happens every two years or every other year.

Biennial is also a noun when it refers to a flowering plant that takes two years to complete its life cycle.

Examples of Biennial in a Sentence

  • Every other year, we have a biennial garden party to raise funds for our youth program.
  • A biennial plant lasts two years from planting to death.

When to Use Semiannual

Do biannual and semiannual mean the same thing? Yes, semiannual is a synonym of biannual. Semiannual means twice every year.

Biannual and semiannual are interchangeable.

Semi- is a prefix that means half in quantity or value, partly, having some of the characteristics of, or quasi-.

Examples of Semiannual in a Sentence

  • We hold an AGM once a year, but we hold the other meetings semiannually.
  • The semiannual meetings are a great opportunity to meet with colleagues from other departments whom you might only see twice a year.

What about Biweekly and Bimonthly?

The meanings of biweekly and bimonthly can be ambiguous, so it’s better to avoid these words if possible.

According to Fowler’s Dictionary of Modern English Usage, “some compounds can only ever mean ‘occurring or continuing for two of the specified units of time’, or ‘appearing every two … ‘, as in bicentennial. Some, however, such as biweekly, bimonthly, and biyearly, can mean that, or they can mean ‘occurring twice in a specified unit of time’: e.g. is a biweekly newspaper available every two weeks or twice a week?”

Merriam-Webster Dictionary also notes that bimonthly and biweekly are ambiguous words “because they are formed from two different senses of bi-:’occurring every two’ and ‘occurring two times.’”

As a result of this confusion, it’s better to be very specific and use words like “twice a week,” “every two months,” “fortnightly,” etc.

Biannual vs. Biennial Quiz

Choose the best word to complete each sentence. The answers are at the bottom of this blog post.

  1. Biannual/Biennial means that something happens twice a year.
  2. Biannual/Biennial means that something happens every two years.
  3. I see her twice a year at the biannual/biennial Brown family reunion.
  4. There are no biannual/biennial gala balls scheduled until next year, so we’ll have to find some other reason to dress up.
  5. In the employee contract, it says that “Employees are subject to biannual performance reviews.” That means the reviews happen twice a year/every second year.

Final Thoughts on Biannual vs. Biennial

By understanding the difference between biannual and biennial, you can avoid being misunderstood when writing and speaking. Not only will your grammar improve, but you’ll be less likely to make costly mistakes like booking a party venue biannually instead of biennially!

Biannual vs. Biennial Quiz Answers

  1. Biannual means that something happens twice a year.
  2. Biennial means that something happens every two years.
  3. I see her twice a year at the biannual Brown family reunion.
  4. There are no biennial gala balls scheduled until next year, so we’ll have to find some other reason to dress up.
  5. In the employee contract, it says that “Employees are subject to biannual performance reviews.” That means the reviews happen twice a year.

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