It is biennial.
Annal
The adjective is quadrennial. (extension of 1-annual, 2-biennial, 3-triennial) (The archaic word for a five-year period is a lustrum.)
Year 1000 was a medieval word. It was approximately in the middle of the Middle Ages. It starts with the letter Y.
There is no word for a 225th year of anything. However there are some names for 200th and 300th years. Bicentenary , Bicentennial - 200th anniversary. Tercentenary, Tercentennial, Triennial - 300th anniversary.
It is biennial.
It is biennial.
You could refer to it as a quarterly event.
Leap Day! :)
biennial
Biannual means twice every year.
It means year or yearly for example anniversary this is a Latin root word.
Centenary means the 100th anniversay, which would be the 100th year.
The word you are looking for is biennial. It does not mean a person who will have sex with anyone but only once every two years.
year
While not specifically "by year", chronological means "in order of occurrence in time"
A biennial is a plant that completes its life cycle in two years, typically flowering and producing seed in the second year. It differs from annuals, which complete their life cycle in one year, and perennials, which live for more than two years.