The Collaborative International Dictionary of English v.0.48:

Rondeau \Ron*deau"\, n. [F. See Roundel.] [Written also
   rondo.]
   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.
      [1913 Webster]

   Note: 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.
         [1913 Webster]

   2. (Mus.) See Rondo, 1.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rondo \Ron"do\, n. [It. rond[`o], fr. F. rondeau. See
   Rondeau.]
   1. (Mus.) A composition, vocal or instrumental, commonly of a
      lively, cheerful character, in which the first strain
      recurs after each of the other strains. "The Rondo-form
      was the earliest and most frequent definite mold for
      musical construction." --Grove.
      [1913 Webster]

   2. (Poetry) See Rondeau, 1.
      [1913 Webster]

WordNet (r) 3.0 (2006):

rondo
    n 1: a musical form that is often the last movement of a sonata
         [syn: rondo, rondeau]