Occurring once every 20 years.

Roget 98: five, quinary^†, quintuple; fifth; senary^†, sextuple; sixth; seventh; septuple; octuple; eighth; ninefold, ninth; tenfold, decimal, denary^†, decuple^†, tenth; eleventh; duodenary^†, duodenal; twelfth; in one's 'teens, thirteenth.    vicesimal^†, vigesimal; twentieth; twenty-fourth etc. n.; vicenary^†, vicennial^†.    centuple^†, centuplicate^†, centennial, centenary, centurial^†; secular, hundredth; thousandth, etc. ... meer laten zien