The Collaborative International Dictionary of English v.0.48:
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. [1913 Webster]WordNet (r) 3.0 (2006):
octosyllabic adj 1: having or characterized by or consisting of eight syllables