Anapest is a metrical foot containing three syllables, the first two of which are unstressed and the last of which is stressed. 

From A Poet’s Glossary

The following additional definition of the term anapest is reprinted from A Poet's Glossary by Edward Hirsch.

A metrical foot consisting of three syllables, two unaccented followed by one accented, as in the words “in a war.” The anapest was originally a Greek martial rhythm and often creates a galloping sense of action, a catchy, headlong momentum, as in these lines from the beginning of Lord Byron’s “The Destruction of Sennacherib” (1815):

The Assyr | ian came down | like a wolf | on the fold, 
And his co | horts were gleam | ing in pur | ple and gold;
And the sheen | of their spears | was like stars | on the sea,
When the blue | wave rolls night | ly on deep | Galilee. 

Other examples of eighteenth- and nineteenth-century anapestic poems in English include [William] Blake’s “Ah! Sun-flower” (1794), [Percy Bysshe] Shelley’s “The Cloud” (1820), [Edgar Allan] Poe’s hypnotic “Annabel Lee” (1849), and [Algernon Charles] Swinburne’s “Before the Beginning of Years” (1865). The momentum of anapests has mostly been employed for comic or ironic effects in modern poetry, as in Thomas Hardy’s “The Ruined Maid” (1901). David Rakoff used anapestic tetrameter, which trots along at four feet per line, for his posthumously published novel, Love, Dishonor, Marry, Die, Cherish, Perish (2013). 

See also meter

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