a. rare. [f. L. undec-im eleven, after decennary.] Given, occurring, or observed every eleventh year, or once in every eleven years.
1785. E. Stiles, U.S. Elevated to Glory & Honour (ed. 2), 45. It appears from an undecennary account laid before parliament in 1776, that the state of commerce between England only and English America, for the eleven years preceding hostilities, was thus: [etc.].
So Undecennial a.
1858. Owen, in Amer. Jrnl. Sci. & Arts, LXXVI. 423. A comparison of the independent evidence of the astronomer and magnetic observer, has shown that the undecennial magnetic period coincides both in its duration and in its epochs of maximum and minimum with the same period observed in the solar spots.
[1864. Webster.]
