Bi- vs. Semi-

There are two suffixes that people often get wrong: semi- and bi-.There it is. Yes, it’s time for a post on grammar (I bet you can’t wait, can you?)

Bi- and semi- are not interchangeable; don’t be confused. Here are the definitions.

Semi-. That means half. To use semi- as a prefix, that would mean that the modified word is reduced in amount or degree. Some examples: Semicircle, Semi-correct, semi-truck.

Bi-. That means two. Using bi- doubles the amount or degree in question. Some examples of bi-: Bicycle, bipolar, bidirectional, etc.

The biggest place that the two are mixed up are when the two are used in conjunction with increments of time. I’ll be happy to clarify:

semi-[time] = twice a [time]

bi-[time] = every two [time]

So, don’t say that you watch the news semiweekly instead of biweekly. If you watch the news biweekly — that is, every two weeks — then you’d be four times later than the chap who watches it semi-weekly — twice a week. Don’t put ‘biannual’ on a big banner advertising that event you host every six months. Similarly, try to avoid buying that bimonthly magazine subscription, I’d say go for the semimonthly one. (But then again, who subscribes to magazines?)

In regards to the hyphens, those really just depend on the word. You’ll have to play it by ear.

Hopefully I’ll start posting semi-daily, as opposed to my bi-monthly habits from before…


4 thoughts on “Bi- vs. Semi-

  1. Ohhhh Bo.
    Biannual actually means occurring twice a year, sweetheart.
    You’re thinking of biennial, which means to occur once every two years.
    Semiannual and biannual are synonyms.
    Bi- can double, but it can also halve, as a synonym to semi-
    It’s one of the nuances of the English language, it’s a wonder anyone ever understands anyone else, haha (:

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