Borrowed from Latin quīnquennālis, with some influence from quīnquennium (“five-year period”).
quinquennial (not comparable)
- Of or related to a five-year period.
1879, F. D. Morice, Pindar, chapter 3, page 25:
By a singular coincidence, the great master of the Dorian lyre was born during the celebration of the Pythia, the quinquennial festival of Apollo […]
quinquennial (plural quinquennials)
- A five-year period.
- A 5th anniversary.