vicennial /vī-senˈyəl/

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

• hard-heartedness
• hard hit
• hard-hit
• hard-hitting
• hard house
• hardier
• hardiest
• hardihead
• hardiheads
• hardihood
• hardihoods
• hardily
• hardiment
• hardiments
• hardiness
• hardinesses
• hardish
• hard labour
• hard landing
• hard landings
• hard launch
• hard launches
• hard left
• hard line
• hardline