The Collaborative International Dictionary of English v.0.48:

Prosody \Pros"o*dy\, n. [L. prosodia the tone or accent of a
   syllable, Gr. ? a song sung to, or with, an accompanying
   song, the accent accompanying the pronunciation; ? to + ?
   song, ode: cf. F. prosodie. See Ode.]
   That part of grammar which treats of the quantity of
   syllables, of accent, and of the laws of versification or
   metrical composition.
   [1913 Webster]

WordNet (r) 3.0 (2006):

prosody
    n 1: the patterns of stress and intonation in a language [syn:
         prosody, inflection]
    2: (prosody) a system of versification [syn: poetic rhythm,
       rhythmic pattern, prosody]
    3: the study of poetic meter and the art of versification [syn:
       prosody, metrics]