novennial
/nə(ʊ)ˈvɛnɪəl
/adjective
1Recurring every nine years.
1.1Lasting for or relating to a period of nine years.We all know what happened at the last one, but the coming one is always a biggie in the novennial cycle as it will have the election of the Presiding Bishop, the primate of the American church who serves a ten-year term.
Origin
Mid 17th century: from late Latin novennis 'nine years old' (from Latin novem 'nine') + -al.