Something that happens every 25 years is referred to as a "quindecennial." This term is derived from the Latin roots "quinque" meaning five and "decem" meaning ten, collectively signifying a period of 25 years. Quindecennial events can include anniversaries, celebrations, or other recurring occurrences.
Quadrenial
decennial Occurring every ten (10) years. Also tenth anniversary
A triennial event happens every three years.
Something that happens every three years is a triennialevent.
Something that happens once a century.
Something that happens every six years is sexennial.
Something that happens every 5 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.
pentennial
tercentennial
Every 100 years is called a century, made up of 10 decades.
An event that occurs every thirty years is called a "triennial" event. However, this term can be misleading since "triennial" technically refers to something happening every three years. For events specifically occurring every thirty years, the term "tricenary" can be used, although it is less common.