All of the actual dictionary resources that I check seem to agree that biweekly and bimonthly originated as meaning every two weeks and every two months (respectively), but that common usage has made the definitions ambiguous. What makes this even odder is that all the dictionaries seem to agree that biannual only means twice a year because there is an entirely separate word, biennual, which means every two years. While I would prefer that everyone stick to the original defined usage (ie. biweekly only means every two weeks and not twice a week), I don't think that there's any chance of that happening.