from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A strophe, stanza, or poem consisting of three lines.
from The Century Dictionary and Cyclopedia
- n. In prosody, a group of three lines; a three-line stanza.
tri- + (di)stich.(American Heritage® Dictionary of the English Language, Fourth Edition)
I should have preferred, indeed, the ante-penultimate tristich as the _finale_ of the poem.