Poetry Guide: Tribrach
A tribrach is a metrical foot used in formal poetry and Greek and Latin verse. In quantitative meter (such as the meter of classical verse), it consists of three short syllables; in accentual-syllabic verse (such as formal English verse), the tribrach consists of three stressed syllables.
The existence of the tribrach has been contested by some writers and it has no entry in the OED but does appear, primarily as a musical form, in some American dictionaries, such as Virginia Tech Multimedia Music Dictionary. Its appearance in English poetry is rare, as it tends to resolve into two disyllabic feet, depending upon the feet that surround it.