1. Occurring every seven years.
2. Consisting of or continuing for seven years.
An event that occurs every seven years.
[From Late Latin septennium, period of seven years, from Latin septennis, of seven years : septem, seven; see septm̥ in Indo-European roots + annus, year; see at- in Indo-European roots.]
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. occurring every seven years
2. relating to or lasting seven years
[C17: from Latin septennis, from septem seven + annus a year]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
sep•ten•ni•al(sɛpˈtɛn i əl)
1. occurring every seven years.
2. lasting or consisting of seven years.
[1630–40; < Late Latin septenni(s) (Latin septuennis) seven years old (sept(em) seven + -enn-, comb. form of annus year + -is adj. suffix) + -al1]
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.