Examples from the Web for intercalation
The periods of intercalation were at first every two years, then three, and lastly four, and eight.
In the days of Numa it consisted of twelve lunar months, with a system of intercalation something like that of the Greeks.
They divide the year into twelve months of thirty days, and add five days by intercalation.
Whenever the intercalation is made there must necessarily be a change in the dominical letter.Our Calendar|George Nichols Packer
It was with a view to that object principally that each Grecian city arranged its calendar and its system of intercalation.