This week’s piece focuses on a couple of words that always cause confusion.

What do you understand by the words biweekly, bimonthly, and biannually? And for bonus marks, what do you understand by bicentenary and bimillenary?

Let’s use biweekly and bimonthly to illustrate the problem. They actually mean nearly the same thing. Or they don’t. Check any dictionary. Bimonthly can mean twice a month or once every two months. Biweekly can mean twice a week or every two weeks. Every two weeks and twice a month are nearly the same thing, aren’t they?

How did we get to this state? (That’s not just a rhetorical question! If you know the answer, please share via a comment!) My best guess is as follows.

The prefix “bi” comes from Latin. Earlier Latin has “di”, which also has Greek and Sanskrit origins. Both mean “twice, doubly, having two”. With words like bicycle, there is no ambiguity—a bike with half a wheel really isn’t going to win the Tour de France, drugs or no drugs. But when we start dealing with periods of time, we’re torn between associating “bi” with the event and associating it with the timespan. Do you make mortgage payments twice in the period, or do two periods elapse between payments?

Given the prefixes’ origins, the problem appears to be thousands of years old.

Every reference book I’ve checked (six to be precise) contains various levels of caution against using these terms. Webster’s offers “confusion is often avoided by…”; Collins and Oxford dictionaries state, “often avoided…”, and the Canadian Press lists preferred terms. The Chicago Manual of Style advises… but I labour the point.

Clear Alternatives

“Semi” is a prefix that doesn’t carry the ambiguity baggage of “bi”. In fact, it has two companions—“demi” and “hemi”—they all mean broadly the same thing. British musicians will know the term hemi-demi-semi-quaver (half of a half of a half of a quaver, which is itself half of a crotchet, which itself is a quarter-note (or a quarter of a semibreve)).

Twice Per…

It would be difficult (and incorrect) to interpret semi-monthly as anything other than twice a month, or more precisely, every half a month. Likewise, semi-annually clearly means twice per year. If you need to talk about twice per week (How often you shower? Check your subordinates’ expense sheets? Swear off the demon drink?), then semi-weekly is the phrase you’re looking for.

It is equally clear if you use the term twice a… or twice per…

Every Two…

Since “bi” is ambiguous, and “semi” is given over to twice per, the clearest way to refer to every two weeks/months/years is to use… you guessed it; every two weeks/months/years.

Note that every other week/month/year is itself ambiguous, as the Mamas and Papas’ song Monday, Monday will attest. “Every other day of the week is fine, yeah.” Those words aren’t referring to Wednesday, Friday and Sunday; it’s the other six days of the week that are fine.

Clear Alternatives For Those With the Vocabulary

Fortnight

This is a word that appears in Canadian and American dictionaries, but which for some reason isn’t understood by some in my circle of Canadian friends. It’s in everyday use in the UK, and according to my research, in Australia and other English-speaking countries.

It’s a useful word. It can be used interchangeably with two weeks as well as in ways that the latter can’t. For example: I get paid fortnightly (or I get paid once a fortnight)

I get paid two-weekly isn’t really elegant.

I get paid once a two weeks is just wrong.

I get paid once every two weeks has more syllables—the tendency these days is to reduce word count and syllable count.

In the UK at least, you can also use the word in a phrase such as, “the cup final’s on Saturday fortnight.” This means that a game to determine the winner of a cup will be played on the Saturday that is two weeks after this coming Saturday.

If you’re interested in etymology, fortnight comes from “fourteen nights”.

Biennial

This is a word that is frequently encountered in gardening literature, where it refers to plants that flower and/or fruit every two years. A festival in Liverpool that is held every two years is called the “Liverpool Biennial”. It can be used in other contexts when referring to a period of two years.

Sennight

This is now an archaic word. Modeled upon fortnight, its origin is “seven nights”. From this you can infer that a sennight is a week. Its versatility matched that of fortnight, but the word fell into disuse in the 19th century, no doubt because it was a difficult word to pronounce and/or liaise and/or elide.

The Long and Short

Follow the encouragement of my reference books, and avoid the prefix “bi” when referring to periods of time. Use “semi” or “twice per” for the shorter-interval interpretation of “bi” and “every two” for the longer-interval interpretation.

Feel free to use fortnight for “two weeks”. As I showed above, it’s a versatile word, and in my opinion, more North Americans need to incorporate it into their everyday vocabulary.

The same goes for “biennial”, although take care when using it in speaking. “Biennial” and “biannual” can sound the same, especially in some accents.

As for sennight—I think its demise was appropriate. It has no advantage over week as far as versatility is concerned; it has twice as many syllables; and it can make for a bit of a tongue-twister in certain phrases.

Please Help Improve Yonder Pedant’s Ramblings

• Did I miss a typo? (I’ll feel bad when you tell me, but I’d rather you did tell me!)
• Did I write something that makes you want to turn green and burst out of your shirt?
• Do you have any better examples that you would share and allow me to use?

If so, please let me know by leaving a comment.