Is it biannually or biennially?

The words bimonthly, biweekly and biannually confuse most people.

Does ‘bi’ mean that something happens once every two weeks/months/years or twice every one week/month/year?

Unfortunately, they can mean both.

In publishing, ‘bimonthly’ is used fairly consistently to mean ‘every two months’.

But it’s best to avoid the ambiguity of ‘biweekly’, ‘bimonthly’ and ‘biyearly’ and use phrases such as ‘twice a week’, ‘fortnightly’ and ‘every two years’.

‘Biannual’, however, means twice a year and ‘biennial’ means every two years. A biennial plant is one that flowers in its second year.

See more grammar tips.