vicennial /vī-senˈyəl/

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

• hummingbird
• hummingbirds
• hummings
• humming-top
• humming-tops
• hummle bonnet
• hummock
• hummocked
• hummocks
• hummocky
• hummum
• hummus
• hummuses
• humogen
• humogens
• humongous
• humor
• humoral
• humoral immunity
• humoralism
• humoralisms
• humoralist
• humoralists
• humorally
• humored