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Bob's Byway: Glossary of Poetic Terms
Calling itself "unique," Bob's is easy to use, with cross-links throughout, phonetic pronunciation guides when necessary, and many examples and quotations. Click on the letter and scroll for the word.
Encyclopedia Britannica
Encyclopedia Britannica: Guide to Shakespeare:couplet
This is a small section of a much larger article on Shakespeare and the Globe Theater that discusses the use of couplets in poetry. Some different types of couplets are discussed (formal or closed, run-on or enjambment, alexandrine,...