from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. Occurring or observed every eleventh year.
from the GNU version of the Collaborative International Dictionary of English
- adj. Occurring or observed every eleventh year; belonging to, or continuing, a period of eleven years; undecennary.
from The Century Dictionary and Cyclopedia
- Belonging or relating to a period of eleven years; occurring or observed every eleven years, or every eleventh year: as, an undecennial festival.
Sorry, no etymologies found.