Hello all!

Today we’re tackling two oft-confusing prefixes. Unlike many of the word pairs we’ve been discussing, these two prefixes are not spelled or pronounced similarly; rather, the root of their confusion is due entirely to the fact that they have overlapping meanings. Now, bi and semi have many meanings, but I want to focus on just those that overlap–namely, when they’re being used as prefixes before some measure of time, such as bimonthly, semiweekly, and so on.

We’ll take monthly as our case in point for simplicity’s sake. Now, semimonthly is the simpler of the two because it has only one meaning: twice a month. Bimonthly, on the other hand, can mean either twice a month or every two months. So what’s the best way to distinguish when to use one and when to use the other? I find that, particularly when you need to include both meanings in your writing, it’s easier to use each prefix for only one meaning, and since semimonthly can only mean twice a month, that leaves bimonthly to take on the role of signifying every two months. So, if you stick to using semimonthly to indicate twice a month (or semiweekly to indicate twice a week, etc.) and using bimonthly to indicate every two months (or biweekly to indicate every two weeks, etc.), you’ll be in good shape.

And how can you remember when to use which? If you can remember that semi also means partial, that can remind you to use semi as your prefix when you’re trying to indicate something that happens partway through the period of time. And that will also help your readers, who will no longer have to guess your meaning!

Until next time!