Bimonthly and biweekly are the two most useless words in the English language. Webster defines bimonthly as: “1) occurring every two months; 2) occurring twice a month.” I’m not kidding. Those are two completely different meanings for the exact same word. How stupid is that? Why in the world do we allow such nonsense to exist? In its definition of the prefix “bi,” Webster has this to say:
Many people are puzzled about bimonthly and biweekly, which are often ambiguous because they are formed from both senses 1b and 2b of bi-. This ambiguity has been in existence for nearly a century and a half and cannot be eliminated by the dictionary. The chief difficulty is that many users of these words assume that others know exactly what they mean, and they do not bother to make their context clear. So if you need bimonthly or biweekly, you should leave some clues in your context to the sense of bi- you mean. And if you need the meaning “twice a,” you can substitute semi- for bi-. Biannual and biennial are usually differentiated.
Like they said, semimonthly is defined as twice a month, so that answers my problem. But I vote for eliminating bimonthly and biweekly from the English language because they are useless.