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1. Relating to or lasting for ten years.
2. Occurring every ten years.
A tenth anniversary.
[From Latin decennium, a period of ten years; see decennium.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
1. (Units) lasting for ten years
2. (Units) occurring every ten years
a tenth anniversary or its celebration
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
de•cen•ni•al(dɪˈsɛn i əl)
1. of or for ten years.
2. occurring every ten years.n.
3. a decennial anniversary.
4. its celebration.
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.