Something that happens every three years is a triennialevent.
Something that happens every six years is sexennial.
Biennial or biannual can refer to something which happens every two years.
the word is novennial....
Semicentennial
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.
Something that happens every three years is a triennialevent.
Something that happens every six years is sexennial.
Bi-yearly
Quarter. At every Quarter of the financial year (every 3 months).
Biennial or biannual can refer to something which happens every two years.
Annual
Frequently
The definition of the word quotidian is something that happens every single day. A good sentence is, he has to deal with the quotidian traffic on his way to work again.
frequent
The word is triennial.
Biennial is a word describing an event that happens every two years.