In Spanish verse, an octosyllable is a line that has its seventh syllable stressed, on the principle that this would normally be the penultimate syllable of a word (Lengua Castellana y Literatura, ed. Grazalema Santillana. El Verso y su Medida, p. 46). If the final word of a line does not fit this pattern, the line could have eight or seven or nine syllables (as normally counted), thus -
In Medieval French literature, the octosyllable rhymed couplet was the most common verse form used in verse chronicles, romances (the romans), lais and dits. The meter reached Spain in the 14th century, although commonly with a more varied rhyme scheme than the couplet. The French octosyllablic verse came to England via the Anglo-Norman poets from the 12th-13th centuries and influenced 4 stress tetrameter verse used in narration (as in Chaucer).