BIENNIUM Meaning of BIENNIUM in English [ bʌɪ'ɛnɪəm ]■ noun ( plural biennia -nɪə or ~s ) a period of two years.Originearly 20th cent.: L., from bi- 'twice' + annus 'year'. Concise Oxford English vocab. Сжатый оксфордский словарь английского языка. 2004