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Webster 1913 Edition
Rondeau
1.
A species of lyric poetry so composed as to contain a refrain or repetition which recurs according to a fixed law, and a limited number of rhymes recurring also by rule.
☞ When the rondeau was called the rondel it was mostly written in fourteen octosyllabic lines of two rhymes, as in the rondels of Charles d’Orleans. . . . In the 17th century the approved form of the rondeau was a structure of thirteen verses with a refrain.
Encyc. Brit.