Does bimonthly mean twice a month or every two months?

The prefix bi- usually means ‘every two’, so bimonthly means ‘every two months’.Semi- means ‘half’ or ‘halfway’, so semimonthly means ‘every two weeks’. However, bimonthly can also mean ‘twice a month’ – but it is rarely used that way. It is best to remember that bi- is “every two” and semi- is “halfway.”