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 sept in the Appendix of Indo-European roots + annus, year; see at- in the Appendix of Indo-European roots.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
The American Heritage Dictionary Blog
Check out our blog, updated regularly, for new words and revised definitions, interesting images from the 5th edition, discussions of usage, and more.