octosyllabic
adjective
oc·to·syl·lab·ic ˌäk-tə-sə-ˈla-bik 
1
: consisting of eight syllables
2
: composed of verses of eight syllables
octosyllabic noun
Word History
Etymology
Late Latin octosyllabus, from Greek oktasyllabos, from okta- octa- + syllabē syllable
First Known Use
circa 1771, in the meaning defined at sense 1