intercalated

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.

To insert anything somewhere (especially between other things), such as an affix into a word. (Compare interpolate.)

Interleaved, formed in distinctly alternating layers.