biennial
adj.
"lasting for two years" (1620s); "occurring every two years" (1750), from Latin biennium "two-year period," from bi- (see bi-) + annus "year" (see annual). The vowel change is "due to the Latin phonetic law according to which the unaccented and closed radical syllable of the second element of compounds, original -ă- becomes -ĕ-" [Klein]. The noun meaning "a biennial plant" is attested by 1770.
〔李〕[bi-=two 二；enni=year 年；-al a.=of…的⇒“of two years 两年的”→] a. lasting two years；once every two years 持续两年的；两年一度的
〔李〕[bi-=two二；enni=year年；-al a.=of……的→“of two years二年的”→] a. lasting two years持续两年的