vicennial /vī-senˈyəl/

1. Lasting, or coming at the end of, twenty years
2. Occurring every twenty years

• midships
• midsize
• mid-sky
• 'midst
• midst
• midstream
• midstreams
• midsts
• midsummer
• Midsummer day
• midsummer madness
• midsummer-men
• midsummer moon
• midsummers
• Midsummer's Day
• midterm
• midterms
• midtown
• midtowns
• mid-Victorian
• midway
• midways
• mid-week
• Midwest
• Midwestern