undecennary

== English == === Adjective === undecennary (not comparable) (rare) Once every eleven years; undecennial. 1783, Dr. E. Stiles, election sermon an undecennary account laid before Parliament === References === “undecennary”, in Webster’s Revised Unabridged Dictionary, Springfield, Mass.: G. & C. Merriam, 1913, →OCLC.