‖n.; pl. Decenniums L. Decennia [ L. ] A period of ten years. “The present decennium.” Hallam. “The last decennium of Chaucer's life.” A. W. Ward.

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 ]