I don't think it is carelessness in this case. The prefix bi can have both meanings and ultimately it comes down to indeterminate parsing: (biweek)ly or bi(weekly), and thus can only be resolved by convention. But both usages have been long established (at least in the US) so we're stuck. This seems far different from the penultimate or literally or hysterical misuses that became a careless norm.
Semiweekly suffers from the same logical discrepancy, but unlike biweekly the convention is well established (though you hardly ever hear the term in the US. In fact before this thread I wouldn't have known which it meant. (other than definitely being the opposite of biweekly... so...))
Semiweekly suffers from the same logical discrepancy, but unlike biweekly the convention is well established (though you hardly ever hear the term in the US. In fact before this thread I wouldn't have known which it meant. (other than definitely being the opposite of biweekly... so...))