'Undecennary' definitions:

Definition of 'Undecennary'

From: GCIDE

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. [1913 Webster]
An undecennary account laid before Parliament. --E. Stiles. [1913 Webster]