The adjective is quadrennial. (extension of 1-annual, 2-biennial, 3-triennial)
(The archaic word for a five-year period is a lustrum.)
Biannual~ this means twice in one yearbiennial~ this means once every two years
Sextennial means "Recurring every six years."
Bicentennial
enneatical
the word is novennial....
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
The word is "millennium".
Sextennial means "Recurring every six years."
biennial
The word is... bicentennial.
tri-annual
Bicentennial
enneatical
the word is novennial....
Semicentennial