A period or cycle of two years; a less common variant or poetic form of biennium.
From Old French 'bienne', ultimately from Latin 'biennium', this is a variant form that appears in specialized or archaic texts, maintaining the sense of a two-year cycle.
This word is so rare that most English dictionaries don't include it—yet it appears in medieval French poetry and documents, showing how alternate forms survive in specialized historical texts long after common usage changes.
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