The Collaborative International Dictionary of English v.0.48:
Octosyllable \Oc"to*syl`la*ble\, a. Octosyllabic. [1913 Webster]The Collaborative International Dictionary of English v.0.48:
Octosyllable \Oc"to*syl`la*ble\, n. A word of eight syllables. [1913 Webster] octothorpWordNet (r) 3.0 (2006):
octosyllable n 1: a verse line having eight syllables or a poem of octosyllabic lines