to insert a day into a calendar, or to insert between or among already existing layers or elements. Every four years we intercalate February 29, otherwise known as Leap Day.
I've always had this strange fantasy of mixing up the months which contain 30 days with the those containing 31 days. It would be an easy mistake to make, wouldn't it? I don't know much about our calendar and why certain months were given a certain number of days to total out to 365 or 366. I imagine that if we had to insert another day into our calendar to, say, balance out dramatic changes in time, adding days to November, February, April, June and September would be an easy change. There's a science fiction story brewing here. I just know it. Dibs!