Definition of septennial in US English:

septennial

adjective

  • 1Recurring every seven years.

    • ‘The breaks would be largely funded by workers saving part of their salary so they can enjoy the septennial sabbatical.’
    1. 1.1 Lasting for or relating to a period of seven years.
      • ‘He said people generally say that Karvy is a septennial plant that is it flowers every seven years.’

Origin

Mid 17th century: from late Latin septennis (from Latin septem ‘seven’ + annus ‘year’) + -al.

Pronunciation

septennial

/sɛpˈtɛniəl//sepˈtenēəl/