Semimonthly means twice a month. In practice, that is often about every two weeks, but not always exactly 14 days apart because months have different lengths.
Bimonthly usually means every two months, or six times a year. That is the clearest meaning to use when you want to avoid confusion.
For example, a company might say, The newsletter is semimonthly, which means readers get two issues each month. A landlord might say, Rent is billed bimonthly, which means a bill comes once every two months.
The confusion happens because bi can suggest both two and every two. In careful writing, many people avoid ambiguity by choosing a clearer phrase, such as twice a month or every two months.
- Use semimonthly for twice each month.
- Use bimonthly for once every two months.
- When precision matters, spell the schedule out.