Something that happens every three years is a triennialevent.
The word Biennial means Every two years
Sextennial means "Recurring every six years."
Biannual~ this means twice in one yearbiennial~ this means once every two years
Sextennial means "Recurring every six years."
The word is "millennium".
biennial
The word is triennial.
The word is... bicentennial.
Bicentennial
enneatical
the word is novennial....