Source : Webster's Revised Unabridged Dictionary (1913)

Octosyllabic \Oc`to*syl*lab"ic\, Octosyllabical
\Oc`to*syl*lab"ic*al\, a. [L. octosyllabus. See {Octo-}, and
   {Syllable}.]
   Consisting of or containing eight syllables.