Annual.
weekly
triannual
An annual event
I think you are asking about a census.
twice-a-day or it can be called semi-diurnal which relates to such occurrences as tides.
It means something that happens every ninth year.
The word is "Biennial".
Quarter. At every Quarter of the financial year (every 3 months).
When something happens 6 times per year, it is referred to as occurring "bi-monthly." This means the event or frequency happens every two months. It is important to note that the term "bi-monthly" can sometimes be ambiguous, as it can also mean twice a month in some contexts. To avoid confusion, it is best to specify whether it is every two months or 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.
Something which happens every second year is termed biennial
Annual