The Collaborative International Dictionary of English v.0.48:

Rhythmic \Rhyth"mic\ (-m[i^]k), Rhythmical \Rhyth"mic*al\
   (-m[i^]*kal), a. [Gr. ????: cf. L. rhythmicus, F.
   rhythmique.]
   Pertaining to, or of the nature of, rhythm
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         Day and night
         I worked my rhythmic thought.            --Mrs.
                                                  Browning.
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   Rhythmical accent. (Mus.) See Accent, n., 6
   (c) .
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