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I was taught that biweekly and bimonthly meant twice a week and twice a month, respectively. I can even reference this in my very old dictiionaries as being correct. I now see definitions in dictionaries that define biweekly as twice a week AND every other week (Random House, Webster’s), and bimonthly as every other month. These “new” definitions are also used in every-day conversation, and can be confusing (I now have reverted to twice a week or every other week to clarify). When did this change? If biannually is always twice a year, why are not bimonthly and biweekly twice a month and twice a week?

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It had started to change by the time I was in library school in 1981, when I was taught that "biweekly" meant once every two weeks, but "bimonthly" could mean either twice a month or once every two months, and we were better off using "semimonthly" to mean twice a month, and leave "bimonthly" to match "biweekly" in meaning.

I don't know if there's a reason other than common parlance. These things evolve.

mara September 13, 2005, 7:17am

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Though I have been at times confused myself in the past, I don't understand any current confusion and am frankly incredulous of differing "past meanings." Bi- is, was, and always will mean 2; semi- means 1/2. Simple enough, no?

JerryB September 15, 2005, 7:34am

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Most dictionaries have always defined “bi” as both two and twice; perhaps this will add to the confusion and incredulity. The below conclusion unfortunately does not account for "biannually", which always means twice a year (verses biennially, meaning every other year). I have conducted some superficial research, and it appears as though this shift occurred between 1970 and 1980, and was brought about by the publication industry (I guess it just took too much printing space to use every other week and every other month). I’m afraid this is something with which I will have to live, considering meanings/definitions of words can and will slowly change through time……Mara is correct in this statement.

nolagranola September 15, 2005, 9:32am

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Webster came through with a wonderfully thorough definition, and an exact timing of when this occurred (over a century ago!!!). I guess my old dictionaries were remiss not to include both definitions. Here's the link to see their explanation.

nolagranola September 15, 2005, 10:21am

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"biweekly" and "bimonthly" mean the exact same thing as "every other week" and "every other month"... there's no change in meaning... gotta remember that in english there at no less than 50 way's to say the same thing :-)

thesplenderinice September 17, 2005, 8:42pm

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Say fortnightly, it is just easier

Anthony September 26, 2005, 2:13am

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Logically speaking, "bi" means "two". "Bicycle" means "2 wheels", "bifocals" means "2 lenses", etc. So why shouldn't "biweekly" and "bimonthly" mean "2 weeks" and "2 months", respectively? Also I always used "biannually" to mean "2 years", and "semianually" to mean "twice a year".

Seems like a reasonable solution to me

Mike September 26, 2005, 4:35am

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Ever bought a bi-monthly magazine or comic book? The issues came out once every 2 months.

Apply that across the board:

Bi-weekly means once every 2 weeks.
Bi-annually means once every 2 years.

If you mean to say "twice in one", then you would use "semi":

Semi-monthly meaning twice in one month. Semi-annually meaning twice in one year.


Robby Love September 26, 2005, 8:06am

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I also use bi-annually, monthly, weekly to mean every other year, month week. Semi... is twice per. It never occurred to me that it would be otherwise, but, guess what? If you check the dictionary, BOTH meanings are listed for each word. Kinda makes the words useless, doesn't it, if they're completely ambiguous? By the way, I'm a pilot, and the FAA refers to Biannual flight reviews as taking place every two years. And, JerryB, I appreciate your comment about bi meaning 2, but is that two months or two PER month? I guess that's the problem...

Anonymous October 26, 2005, 1:13pm

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I have always used bi-annually as meaning every six months, and that was what I was taught. I've completely reverted to using "every six months" because of confusion both when I used it in my old-fashioned way, and when I tried using it in the every 2 years way!

Lana October 27, 2005, 1:29am

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Well this has helped us at Third Eye Design very much...there was much "bi-annual" confusion. Does it mean every 2 years, or 2 times a year? well now we know. Vicki did however have the right answer all along whilst Jamie unfortunetly was one of the mis-let few.

stewart November 7, 2005, 6:37am

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As for yearly, my Webster's Collegiate (1965) is clear in its advice: every 2 years is biennial, twice per year is biannual. As for weekly and monthly, since the definitions are ambiguous, I agree with those who simply choose to state twice per week, every 2 weeks, etc.

Randy November 11, 2005, 1:38pm

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Biweekly and bimonthly are NOT the same thing even if you define bimonthly as "twice a month". "Twice a month" is not equivalent to "every two weeks." There are 24 "bimonthly" periods in a year but there are 26 "biweekly" periods.

nutter February 4, 2006, 9:50pm

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Bi-monthly vs Semi-monthly (what confusing and misunderstood terms) - I agree with Mike's (Sept. 2005)definitions - I also think wages that are paid bi-weekly are actually paid every 2 weeks; wages that are paid semi-monthly are paid on the 15th & 30th.

Ada August 17, 2007, 8:53am

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Nutter, to whom exactly is your comment addressed? No one was claiming that biweekly and bimonthly are the same.

Anonymous August 20, 2007, 4:19am

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...or biweekly and semimonthly.

Anonymous August 20, 2007, 4:22am

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i thought biweekly and bimonthly both meant twice a month/every two weeks ...

i have no name September 4, 2007, 11:51am

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It helps if you read the whole thread before jumping in. With that in mind, I will jump in...
bi-weekly and bi-monthly and ambigous. You can try to insist that they should mean either TWO or TWICE (big difference between the two), but they mean both! If you think it is obvious it should mean either TWO or TWICE you are asking for trouble - and good luck trying to get the billion English speakers in this world to follow your lead. The simplist solution is not to use these words.

foldnil October 4, 2007, 8:18pm

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All the comments are just what I needed to clarify everything!

john.morgan42 April 14, 2008, 10:38pm

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Or you could waste the extra half a breath and say "twice a week"?

Dan September 18, 2008, 12:49pm

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Well, it would seem that everyone has thier own take on Bi. We all seem to agree that it means two, and the semi=half makes sense as well.
To put gas on the fire, would Bisexual mean liking 1/2 male and 1/2 female, or should it mean liking 2 sexes?
So, semisexuals are attracted to half a sex?
Lordy! Seems the line blurrs the closer to you get to it!

W1x_Styx December 4, 2008, 4:25am

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sorry *their

W1x_Styx December 4, 2008, 4:27am

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All of the actual dictionary resources that I check seem to agree that biweekly and bimonthly originated as meaning every two weeks and every two months (respectively), but that common usage has made the definitions ambiguous. What makes this even odder is that all the dictionaries seem to agree that biannual only means twice a year because there is an entirely separate word, biennual, which means every two years. While I would prefer that everyone stick to the original defined usage (ie. biweekly only means every two weeks and not twice a week), I don't think that there's any chance of that happening.

normwray August 5, 2010, 1:26pm

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I love this never goes away. I was raised in the UK and have lived in the US for the last 14 years, and it still creates confusion when communicating across the pond.

My old UK dictionary has both "every two" or "twice per" listed, and it depends on whether the term was being used as an adjective or an adverb.

Many people refer to the commonly used biweekly [adj] publications as proof that its "every two," yet my US company gives me a bimonthly [adj] paycheck twice per month (their term not mine).

I find most confusion occurs around biweekly [adv] meetings. UK tends to see it as "twice per" and US as "every two." Even though most know what the other is saying, there is always need to clarify the intent. Fortnightly doesn't work outside of the UK so that's not an option either.

To further make a point on how confusing it is (in the UK) a biweekly meet is every two weeks, because a "meet" is a noun typically used in Fox Hunting.

I have given up listening to who is right and wrong, and at the end of the day who really cares? Its a pointless discussion as you will never convince the other person they are wrong. You might gather all the data to prove you are right, yet the other person will find an equal amount of data to prove you wrong. Its just not worth it.

My advice is to explicitly state your intent, otherwise many hours will get wasted and worse you may come off looking like a complete idiot if you try to push an argument you can't win in the other persons mind.

Case in point, if you are reading this post, ask yourself why you are here and how many other posts did you read before this one? If you are not convinced its a bad idea to push for one or the other...continue searching ;-)

Not this topic again March 25, 2011, 5:14pm

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Normwray, I think you mean biennial, not biennual.

porsche March 26, 2011, 12:52pm

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Please do not use "semi [period]" to mean "twice per [period]" or "once per half [period]". For comments here, it seems to have traction in the US but it certainly does not have traction outside the US. "Semi" means "partially", with implications of 100% > semi > 50% (e.g. something that is more soft than hard is semi-soft. It's more than half soft - or it'd be semi-hard - but less than 100% soft). In terms of time, semi can mean something like "not quite a [period]" e.g. semi monthly = not quite monthly. Given that this is frequency, not quite monthly does not mean "more often than once a month" it means "not as often as a month". So semi still means less often than monthly, but without a known or exact cadence. Long story short, semi is nowhere near accurate enough to mean "twice" or "half" or anything to do with a specific number.

Camryn.NZ June 13, 2012, 9:05am

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BTW, I know that "semi" has an original Latin meaning of "half" but it has lost precision in English e.g. semi permanent != half permanent.

Camryn.NZ June 13, 2012, 12:35pm

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