Well, I'm livid now. I just learned that not everybody uses the same definition as me for terms like biweekly, bimonthly, and biannually.
For years, I've labored under the understanding that bi- means two of while semi- means half of, so that bimonthly is every two months while semimonthly means twice a month.
Not so for everyone. Some people use bimonthly to mean twice a month. In fact, online dictionaries have shown the definition to mean either twice a month or every two months. That basically means bi-[time period] is useless in conversation now. Except for biennial, which has a clear definition.
I wonder how these are handled in legal papers. I imagine that bi- is avoided entirely.
My world view has been shattered.