Definition of "tribrach"

For your foote tribracchus of all three short, ye haue very few trissillables.

1589, George Puttenham, The Arte of English Poesie, book ii, chapter xiii (Arb.), page 133

We may vse a Spondee or Iambick and sometime a Tribrack or Dactile.

1602, Thomas Campion, chapter IV, in Observations in the Art of English Poesie, page 11

Tribrachus or Tribrachys, (Gr[eek]) a Foot in Greek and Latin Verſe, conſiſting of three ſhort Syllables; as Pŏpŭlŭs.]

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Of all the resolved feet, the Tribrach in Trochaic verse with its ictus on the first syllable ⏑́⏑⏑ is most readily recognised by the ear as equivalent to the Trochee.

1827, the Rev’d Canon James Tate, An Introduction to the Principal Greek Tragic and Comic Metres in Scansion, Structure, and Ictus (second edition, 1829), chapter xi: “The Ictus of the long Trochaic of Tragedy”, §5 (page 23)

If the range of pure tribrachic measure, or of tribrachs intermingled with trochees, appears much wider in our song-books than in volumes of poetry written to be read.

1866, John Stuart Blackie, Homer and the Iliad, volume I, page 401

The plain tribrach is frequent in every one’s reading.

1885, Thomas Dwight Goodell, “Quantity in English Verse”, in Transactions of the American Philological Association, XVI, page 88