biennial and biannual, althou biannual could also mean twice a year
Something that happens every six years is sexennial.
Semicentennial
the word is novennial....
The word "biennial" means an event that either lasts for two years, or it happens every two years.
Biennial is a word describing an event that happens every two years.
Something that happens every three years is a triennialevent.
The word is triennial.
Biennial or biannual can refer to something which happens every two years.
If something happens twice a month it is called biweekly because it happens every other week and a month has 4 weeks. there is also bimonthly which is every other month but not really a direct word for something that happens twice a month.
Quinquennial = something that happens every 5 years. Lustral = also something that happens every 5 years or we could invent: semi-Decennial: where semi is half and Deccennial happens every 10 years.
That word is "event."
semimonthly