The Collaborative International Dictionary
Undecennary
Undecennary \Un`de*cen"na*ry\, a. [L. undecim eleven (unus one + decem ten) + -ennary as in decennary. Cf. Undecennial.] Occurring once in every period of eleven years; undecennial.
An undecennary account laid before Parliament.
--E.
Stiles.