noun-modifying (irregular)
quadrennial; recurring every four years
Used as a prenominal modifier for events, plans, or periods that occur or span four years. Common in official contexts like 四か年計画 (four-year plan).
市は新しい四か年計画を発表した。
The city announced a new four-year plan.
この四か年契約は来月で切れる。
This four-year contract expires next month.
Variant using the Arabic numeral 4.
Variant using the Arabic numeral 4 and the kanji 箇.
Variant using the Arabic numeral 4 and the katakana カ.
Variant using the Arabic numeral 4 and the small katakana ヵ.
Variant using the Arabic numeral 4 and the small katakana ヶ.
Variant using the Arabic numeral 4 and the full-width katakana ケ.
四年 is the simple noun meaning 'four years' (a duration), while 四か年 is a prenominal modifier used in formal or official contexts to describe something that spans or recurs every four years.
Compound of 四 (four) + the counter か年 (years), where か is a counter suffix derived from 箇. The reading よん is the on'yomi of 四, and ねん is the on'yomi of 年.