Every eight years, a variety of notable events occur, including U.S. presidential elections, which take place in even-numbered years. Additionally, some countries hold elections or referendums on a similar cycle. In sports, certain tournaments, like the Summer Olympics, also occur every four years, contributing to an eight-year cycle for some events. Moreover, various environmental phenomena and cycles, such as certain species' life cycles or economic trends, can also repeat on an eight-year basis.
A triennial event happens every three years.
Something that happens every six years is sexennial.
Beginning with the August 8, 2008 summer Olympics nine new events were added.
That only happens when Easter falls on April 8, which happens on average once every 35½ years.
Something that happens every three years is a triennialevent.
Something that happens once a century.
As far as I know, nothing special happens every 100,000 years. A full precession cycle takes about 26,000 years.
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.
It happens every 200 years.
the Olympics
The Olympics.
Something that happens every 5 years