1. the insertion of something between other things or into a sequence
Usage: formal
2. the addition of an extra day, month, or period to a calendar to keep it aligned with astronomical cycles
Usage: calendar systems; astronomy
3. the process of inserting atoms, ions, or molecules between the layers of a crystalline structure
Usage: chemistry; materials science

Examples

• The intercalation of leap days keeps our calendar synchronized with Earth’s orbit.
• February 29th is added through intercalation every four years.
• The intercalation of lithium ions between graphite layers occurs in battery operation.
• Ancient calendars required frequent intercalation to maintain seasonal accuracy.
• The intercalation of additional verses changed the poem’s original structure.
• Scientists study the intercalation of molecules in clay minerals.
• The Roman calendar underwent several intercalation reforms throughout history.