1. Occurring once every 20 years

See also: twenty

• Callirhoe involucrata
• Callirhoe triangulata
• Callisaurus
• Callisaurus draconoides
• Callistephus
• Callistephus chinensis
• callisthenics
• Callisto
• Callithricidae
• Callithrix
• callithump
• callithump parade
• callithumpian
• Callitrichaceae
• Callitriche
• Callitris
• Callitris calcarata
• Callitris cupressiformis
• Callitris endlicheri
• Callitris glauca
• Callitris glaucophylla
• Callitris parlatorei
• Callitris quadrivalvis
• Callophis
• Callorhinus