Biannual vs. semiannual

[mazzer]

Biweekly means once every two weeks.
Bimonthly means once every two months.
Biannually means twice a year.

I understand that "annually" is not the same as "yearly," and thus the departure, but:

The big bad dictionary gives the definition of biannual as: "twice a year; semiannual." How can these two words mean the same thing? Their prefixes have opposite meanings.

Something strange has happened here. Any help?

[Chas.E]

The correct usage would be "biennial."

Lexicographers make mistakes too.

[KneadToKnow]

Originally posted by chriszarate
How can these two words mean the same thing? Their prefixes have opposite meanings.

inflammable = flammable :)

Regardless of how the parsed-out morphemes should add up, if somebody is using "biannual" to mean "semiannual" then there's not much you can do about it. The simple fact of the matter is this: a lot more things happen twice a year than happen every two years, especially in nature.

I think the thought process is along these lines, though: if a bicycle is one thing with two parts, then biannual must mean one year divided into two parts. I personally try to avoid all such confusions by using the expression "twice a year." :)

[BobT]

According to the OED "Biannual" as an adjective means "half-yearly" and as a noun it has the same meaning as "Biennial", which means every two years.

"Semiannual" as both an adjective and a noun means "twice a year".

"Biennial" is a very old word dating back to the 17th century, but "biannual" didn't come around until late in the 18th century.

The state of California issues a publication called "Used Oil Recycling Rates". It is called "A Biannual Report". And it was released every two years. It is cataloged as "biennial."

A different office in the same state agency issued something titled "Biannual report on redemption and recycling rates"
It is cataloged as a "semiannual" and comes out every six months.