from The Century Dictionary.
- Consisting of three semeia; trisemic.
- noun A trisemic time or syllable.
Sorry, no etymologies found.
Most obviously, the four lines of poetry are set to four distinct musical phrases, each the same length twelve units of time and each closing with a "triseme" preceded by another long duration.
Note that the duration indicated is that of the syllable, not of the pitch, so that a "diseme" may include two pitches (as in the second line) and the "triseme" one, two, or three (as at the end of each line).
The horizontal dash - indicates a "dissme", worth two units, and the horizontal dash with an upward stroke to the right is a "triseme", worth three.