1) Type of verse 2) Verse 3) Verse line 
The octosyllable or octosyllabic verse is a line of verse with eight syllables. It is equivalent to tetrameter verse in iambs or trochees in languages with a stress accent. Its first occurrence is in a 10th-century Old French saint`s legend, the Vie de Saint Leger; another early use is in the early 12th-century Anglo-Norman Voyage de saint Brenda....
• (n.) A word of eight syllables. • (a.) Octosyllabic.
Oc'to·syl`la·ble adjective Octosyllabic. 
[n] - a verse line having eight syllables or a poem of octosyllabic lines
noun a verse line having eight syllables or a poem of octosyllabic lines