Octosyllable a. : Octosyllabic.

Octosyllable n. : A word of eight syllables.

Example:


Taxonomy
octosyllable, free encyclopedia, syllables, octosyllabic, syllable line, Princeton, penultimate syllable, couplet, Princeton Encyclopedia of Poetry and Poetics, search, tetrameter, languages, commonly used, principle, Lengua Castellana y Literatura, Grazalema, Santillana, Medida.

Defination from the web:
octosyllable is a line that has its seventh syllable stressed, on the principle that this would ... In Medieval French literature, the octosyllable rhymed couplet was the most common verse form used in verse chronicles, romances (the romans), lais and dits. ...