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Biennial describes something that happens once every two years, like a biennial conference held every second year. It is also used for a type of plant that lives for exactly two years, growing leaves in the first year, then flowering, making seeds, and dying in the second. Be careful: this word looks a lot like biannual, which usually means twice a year, the opposite kind of frequency. Because of this confusion, many careful writers just avoid biannual altogether and write 'twice a year' instead.
兩年一次的；二年生（植物）
組成bi- (two) + enni (from Latin 'annus', year) + -al (relating to). Literally 'relating to two years.'
同家族的字
- annualsame root annus, meaning happening once a year
- centennialsame root annus, meaning happening once every hundred years, or a 100th anniversary
原始詞典資料4 筆記錄
以下是外部詞典記錄的用法，原文照列，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
biennialadj/baɪˈɛn.i.əl/
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Happening every two years.
- This is a marked difference from the task force’s previous guidance, which was to start biennial mammograms by age 50.
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Lasting for two years.
biennialnoun/baɪˈɛn.i.əl/
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A plant that requires two years to complete its life-cycle, germinating and growing in its first year, then producing its flowers and fruit in its second year, after which it usually dies.
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An event that happens every two years.
- The famous Biennial was won by Earl of Dartrey, a light, peacocky horse, who was, perhaps, better than he looked.
資料來源：英文維基詞典 English Wiktionary（CC BY-SA 4.0）。 原文照列，未經改寫。