a. [ See Decennary. ] Consisting of ten years; happening every ten years; as, a decennial period; decennial games. Hallam. [ 1913 Webster ]

n. A tenth year or tenth anniversary. [ 1913 Webster ]

a. [ L. duodecennis; duodecim twelve + annus year. ] Consisting of twelve years. [ R. ] Ash. [ 1913 Webster ]

a. [ See Undecennary, and cf. Decennial. ] Occurring or observed every eleventh year; belonging to, or continuing, a period of eleven years; undecennary; as, an undecennial festival. [ 1913 Webster ]