intercalate

To insert (a day or month) in a calendar.

To insert, interpose, or interpolate.

In chronology, to insert in the calendar by proclamation or authority, as an extra day or month. See intercalary, 1.

Hence To insert between others; introduce interstitially; interject or interpolate, as something irregular or unrelated.

To insert, as a day or other portion of time, in a calendar.

To insert among others, as a verse in a stanza; specif. (Geol.), to introduce as a bed or stratum, between the layers of a regular series of rocks.

To insert an extra, leap, day into a calendar in order to maintain synchrony with natural phenomena.

To insert an extra month into a calendar for the same purpose. The Hebrew calendar has such a month.

To insert a substance between two or more molecules, bases, cells, or tissues.

insert (days) in a calendar