Couplet - a pair of successive lines of verse, especially a pair that rhymes, that are of the same metrical length, and form a single unit. The term is also used for lines that express a complete thought or form a separate stanza. Couplets are usually written in decasyllabic lines. A closed couplet is one that is logically and grammatically complete.
The word comes from the French diminutive of couple which was derived from the Latin copula, meaning “a band or bond.”
The form was first used by Chaucer in the Fourteenth Century. Tudor and Jacobean poets and dramatists used it as a variation of blank verse and to round off a scene or act. The couplet eventually evolved into the heroic couplet, which was rhymed iambic pentameter and popular in the Seventeenth and Eighteenth Centuries. Nineteenth-Century Romantic poetry used the couplet, as do epigrams.
Shakespeare used this form in the concluding lines of his sonnets. Chaucer used it in his “Merchant’s Tale” within The Canterbury Tales:
Whilom ther was dwellynge in Lumbardye
A worthy knyght, that born was of Pavye,
In which he lyved in greet prosperitee;
And sixty yeer a wyflees man was hee,
And folwed ay his bodily delyt
On wommen, ther as was his appetyt…
lines 1 – 6
see: epigram, stanza, sonnet