(I wrote this to Anu and he, or his auto-reply, directed me to the message boards. My question was inspired by a weekly theme, but the weekly theme board doesn't seem to be very popular.)

I was wondering if you could help me with some time-related words. I hope you haven't covered this in an earlier email, if you have let me know and I'll find it in the archives.

It's the use of "semi" and "bi" as prefixes. Looking at the prefixes, I believe that "semi" means "one-half" and "bi" means "two". So, I would have thought that bi-annual would mean "twice a year" while semi-annual would mean "once every two years" (literally, "one-half every year"). Same with bi-weekly and semi-weekly and probably others as well.

However, there seems to be no consensus on this in daily conversation. Even dictionary.com seems to have conflicting definitions, although I suspect that all commonly used meanings of a word are provided, even if one is not used properly when looking at its original meaning:
bi·an·nu·al adj.
Happening twice each year; semiannual.
Occurring every two years; biennial.

Can you shed any light on this? Is one way more proper than another? Or do we have to accept that a "time" word can, with equal validity, indicate two entirely different frequencies and hence is useless, in my mind, since it does not convey a consistent thought to the entire audience?

Thanks,
Joe