noun-modifying (irregular)
quinquennial; recurring every five years
Used as a prenominal modifier in formal or administrative contexts, such as government plans or reports. Often appears in phrases like 五箇年計画 (five-year plan).
政府は新たな五箇年計画を発表した。
The government announced a new five-year plan.
五箇年ごとに大規模な調査が行われる。
A large-scale survey is conducted every five years.