octennial /ok-tenˈyəl, -i-əl/

1. Happening every eighth year
2. Lasting eight years

octennˈially adverb

• nightfires
• night-fisheries
• night-fishery
• night-flies
• night-flower
• night-flowering
• night-flowers
• night-fly
• night-flying
• night-foe
• night-foes
• night-fossicker
• night-fossickers
• night-foundered
• night-fowl
• nightgear
• nightgears
• night-glass
• night-glasses
• nightgown
• nightgowns
• night-hag
• night-hags
• nighthawk
• nighthawks