The Collaborative International Dictionary of English v.0.48:
Decennium \De*cen"ni*um\, 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. DecennovalWordNet (r) 3.0 (2006):
decennium n 1: a period of 10 years [syn: decade, decennary, decennium]