1. occurring every eight years or lasting for eight years

1. an event or celebration that occurs every eight years, or the eighth anniversary of an event

Examples

• The university holds an octennial reunion for graduates from each class.
• The octennial celebration marked eight years since the organization's founding.
• They planned an octennial festival to commemorate the historic event.
• The octennial cycle of the conference brings scholars together every eight years.
• This year marks the octennial of the company's establishment.
• The octennial review examines progress made over the past eight years.