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Biannual vs Biennial? When to Use Each and When Not To

Biannual vs Biennial? When to Use Each and When Not To

Despite having fairly discrete spellings and relatively unique pronunciations, specific terms in the English language seem to carry the same meaning. In other words, most people assume those words mean the same, only to find out their mistake later. The words “biannual” and “biennial” are two such terms that seem like the same, but they aren’t.

The word “biannual” means “once every six months”; and “biennial” means “once every two years”. They are two unique words with distinct meanings. Use the term “biannual” to describe a meeting that’s held twice a year. If an event is held once every two years, use the term “biennial” to denote the same.

Keep reading to learn more about the meanings of the two terms, how they are different from each other, alternate words for them both, and lots more.

Biannual word in the dictionary

Biannual – Definition

Composed of two individual words, “bi” (which means “two”) and “annual” (yearly or every year), the term “biannual” means “two times a year”. When used with the temporal word “annual”, “bi-” means “every two”. Commonly used synonyms of the word include “biyearly” and “semi-annual”.

To illustrate, if an HVAC company suggested a “biannual” inspection of your air conditioner, it means you must get the appliance professionally inspected once every six months.

“Biannual” could also mean “once every two years”, if reputable online dictionaries such as and were to go by.

Biennial – Definition

The word “biennial” means “once every couple of years”. The term that sets apart “biennial” from “biannual” is “-ennial”.

Suppose a heating company recommends a “biennial” inspection of your air conditioner. In that case, it means the service technicians will visit your place once every two years for cleaning and a thorough inspection of the device.

The root word “-ennial” can be combined with a few other words or prefixes to form new terms, which include:

  • Perennial: Throughout the year, as “per” means “through”.
  • Centennial: “Centi-” stands for “hundred”. Therefore, a “centennial” means “once a hundred years”.
  • Sesquicentennial: “Sesque” means “1.5 times more”. Therefore, a “sesquicentennial” means “once every 150 years”.

P.S. Both “biannual” and “biennial” have their roots in the Latin term, “annus”, which translates as “year”. Also, though primarily used as adjectives, both “biannual” and “biennial” can also be used as nouns.

The Confusion Between “Biannual” and “Biennial”

As mentioned above, “biannual” and “biennial” mean two different things, and they should, therefore, not be used interchangeably in texts or conversations.

Unlike the terms “biweekly” and “bimonthly”, it’s not easy to differentiate between “biannual” and “biennial” – since not many may know what the term “biennial” means.

The prefix “bi-” is self-explanatory, even to individuals with basic English knowledge. Similarly, the words “weekly” and “monthly” also easily give away their meanings. When the prefix “bi-” is attached to the two terms, it is clear that “biweekly” means “once every couple of weeks” and “bimonthly” means “once every two months”.

With the adjectives “biannual” and “biennial”, however, things aren’t that evident. “Biannual” is relatively straightforward, but “biennial” isn’t, since “-ennial” is not as common a word as “weekly”, “monthly”, or “annual” despite being a valid English term.

As a result, people who encounter the term “biennial” for the first time feel inclined to believe it’s an alternate word for “biannual” as “-annual” and “-ennial” do not sound very different.

If you’re getting confused between “biannual” and “biennial”, use “semi-annual” instead of “biannual”.

Using “Biannual” in Writings

The term “biannual” is widespread in business documents as companies usually review their financials once every two years, at least. The word is also commonly used outside of the business world.

However, as mentioned above, “biannual” could mean “once every couple of years”, if the context for the word is set. But the context is not always clear, and it may not be that difficult to get confused by the ambiguity associated with the term.

In the following sentence, for example, it’s not clear what “biannual” means:

  • The meeting is biannual.

It could mean the meeting takes place “two times a year” or “once every 24 months”.

Writers who use “biannual” with its alternate meaning use the term “semi-annual” to mean “once every six months”. This alternate meaning for the word “biannual” is not universally accepted and could be deemed incorrect by many native English speakers.

Regardless, the word “biannual” has evolved or “devolved” to assume its secondary meaning.

biennial plant with royal blue flowers

Should You Hyphenate “Biannual”, as in “Bi-annual”?

“Biannual” is at times written as “bi-annual”. However, the big question is whether adding a hyphen to the word changes the meaning of the term or indicates something else.

Hyphenating a word like “biannual” could seem logical, as “bi” and “annual” are two individual words. However, hyphenation rules state root words and prefixes must be hyphenated only when not using a hyphen can create confusion.

For instance, if adding a prefix and root word could make the resulting word look like a spelling error, a hyphen would help. For example, a word like “semi-independent” needs a hyphen because the prefix “semi” ends with the letter “I”, and the root term “independent” begins with the same letter too.

Without the hyphen, it won’t look right – for example, “semi-independent”. Other similar words that should be hyphenated include “semi-invalid” and “semi-infinite”.

With “biannual”, there is no such visual sore as “bi” and “annual” have different ending and starting letters, respectively. Long story short, “bi-annual” is an incorrect usage of the hyphen, like how “semi-independent” is not a proper English word.

Using “Biennial” in Writings

Besides using it to denote events or occurrences that happen once every couple of years, the term “biennial” could also be used for describing a plant that takes a couple of years to grow to its full potential – from seed to fruition. For example:

  • The onion plant is a biennial.

Kindly note, in the sentence above, “biennial” is used as a noun. Here is another example sentence where the word is used as a noun:

  • The most popular antique exhibition is the Florence biennial.

The above sentence can be modified to turn “biennial” into an adjective from a noun.

  • The Florence antique exhibition is the most popular biennial event of its kind.

Example Sentences with the Word “Biannual”

The following are sentences incorporating the term “biannual”:

  • The biannual meeting is conducted every March and September.
  • Certain aspects about the biannual NYFW stay reassuringly the same.
  • This month the biannual magazine’s third issue was launched.
  • The winning idea for the biannual student competition was announced earlier this week.
  • The company held biannual conferences.
  • A biannual journal is a journal published two times a year.
  • The sessions were held biannually during the first decade.

Example Sentences with the Word “Biennial”

Here are sentences with the word “biannual” and some variations of the term:

  • Our garden has biennial flowers.
  • It is the first of the series of biennial fairs.
  • The company hosts the family picnic biennially because the pavilion can be reserved only every other year.
  • Congressional elections take place biennially.
  • The biennial school appropriation amounts to $25,000,000.
  • The plant is truly a biennial, but it grows as freely as a perennial.
  • The expenditure and receipts are computed for biennial periods.
  • The voter registration process happens biennially.

Using “Bi” Instead of “Semi”

The meaning of “bi-” has already been discussed above. What “semi-” means, however, is “half”. And when used with a temporal term, such as “annual”, it means “twice”. For example:

  • The semi-annual meetings will be held in February and August.

The confusion between the two prefixes arises because both relate to “two”. Though “semi-annual” can be used instead of “biannual”, the usage may not always be appropriate.

As mentioned above, “bi-” could also mean “once every (given period)”. In other words, “biweekly” could mean “once every couple of weeks” or “two times a week”; and “bimonthly” could mean “once a couple of months” or “two times a month”.

The prefix “semi-“, however, always means “half”. In other words, “semi-weekly” is “twice a week”, and “semi-monthly” means “twice a month” only.

To avoid the confusion surrounding “bi-“, replace the term with the word’s actual description. For example, instead of writing “I visit my mom bimonthly“, write “I visit my mom every two weeks“.

“Biyearly” or “Biannual”?

The words “biannual” and “biyearly” mean the same thing. The two terms, therefore, can be interchangeably used. Compared to “biyearly”, however, “biannual” is a lot more commonly used term. Here is a sentence with the word “biyearly”:

  • The line sale takes place biyearly, which is opportune as I prefer replacing my sheets once every six months.

A similar confusion lies with “semi-annual” and “semi-yearly”, as both mean “once every six months”.

biennial written on a keyboard


The adjectives “biannual” and “biennial” are remarkably similar despite being quite different. Even professional writers and editors could end up mistaking one word for the other. These errors have a fair bit to do with the terms being more familiar to the world of business and finance.

Therefore, compared to regular copywriters, writers who excel at writing business and finance pieces are least likely to confuse between the two terms. But if you don’t have a business background, that’s still no excuse to blunder with the two words – especially as you now know the meanings of the terms and the linked discrepancies.