The Grammarphobia Blog

The scoop on “bi” and “semi”

Q: I was taught in school that “bimonthly” meant “every other month” and “semimonthly” meant “twice a month.” But nobody seems to remember the difference anymore. In fact, many companies don’t even use those terms now. They say “every other month” or “twice a month” instead. Do you think that’s right?

A: I can understand the problem the companies have. As I wrote in Woe Is I, the prefix “bi” means two and “semi” means half, but in practice “bi” sometimes means “semi” and “semi” sometimes means “bi.” For example, “bimonthly” can mean every two months OR twice a month, depending on the dictionary you consult. “Biweekly” can mean every two weeks OR twice a week. “Biennial” means every two years, but “biannual” can mean every two years OR twice a year.

So it’s probably better to avoid misunderstandings and say “every other month” or “twice a month” if that’s what you mean.