A form of poetical composition invented in the 13th century, consisting of 14 decasyllabic or hendecasyllabic iambic lines, rhymed according to two well-established schemes which bear the names of their two most famous exponents, Shakespeare and Petrarch. The Shakespearian sonnet consists of three four-lined stanzas of alternate rhymes clinched by a concluding couplet; the Petrarchan of two parts, an octave, the first eight lines rhymed abbaabba, and a sestet, the concluding six lines arranged variously on a three-rhyme scheme.