Rhythm, n.
Etymology: [F. rhythme, rythme, L. rhythmus, fr. GR. Stream.]
1. In the widest sense, a dividing into short portions by a regular succession of motions, impulses, sounds, accents, etc., producing an agreeable effect, as in music poetry, the dance, or the like.
2. (Mus.)
Movement in musical time, with periodical recurrence of accent; the measured beat or pulse which marks the character and expression of the music; symmetry of movement and accent. Moore (Encyc. )
3. A division of lines into short portions by a regular succession of arses and theses, or percussions and remissions of voice on words or syllables.
1 more senses
4. The harmonious flow of vocal sounds.
Shades of meaning
Fernald has no entry of its own for rhythm; he lists it under meter.
Where he writes about it:
Euphony is agreeable linguistic sound, however produced; meter, measure, and rhythm denote agreeable succession of sounds in the utterance of connected words; euphony may apply to a single word or even a single syllable; the other words apply to lines, sentences, paragraphs, etc.; rhythm and meter may be produced by accent only, as in English, or by accent and quantity combined, as in Greek or Italian; rhythm or measure may apply either to prose or to poetry, or to music, dancing, etc.; meter is more precise than rhythm, applies only to poetry, and denotes a measured rhythm with regular divisions into verses, stanzas, strophes, etc. — from meter